CBS’ hit comedy series The Big Bang Theory has been on for a very, very long time. Debuting all the way back in 2007, it has outlived even some of the most famous sitcoms of the modern era. The show’s staying power may be attributed to the brilliant writing and masterful acting, though it could also be said to appeal to a certain niche audience that typically doesn’t get much love from prime time network executives.

That said, much like any show that may or may not have overstayed its welcome, the plot of The Big Banth Theory is slowly starting to lose itself and teeter ever closer into jumping-the-shark territory. For instance, the marriage of Leonard and Penny seems very much like something that should have taken place during the show’s finale, not to mention the bizarre marriage of Sheldon Cooper, the show’s famous anti-socialite.. Yet, with season twelve laying somewhere along the horizon, fans have little choice but to wait and see what will happen.

That isn’t to say that the show is necessarily declining — it continues to draw large TV audiences nearly twelve years after it first aired — but it does mean that some weird, potentially contradictory elements are starting to pop up. With a total of 255 episodes and a full on spin-off show about his childhood, fans have started to notice a few issues with everyone’s favorite nerd Sheldon Cooper.

We all know that he’s already a bit abnormal, but here are the 20 Things About The Big Bang Theory's Sheldon That Make No Sense.

His Criminal Background

Viewers are no doubt aware that, despite his relatively mild-mannered persona, Sheldon can, at times, be a bit overbearing. Demonstrating a total lack of relationship skills and committing social faux pas so regularly that his presence has become nearly unbearable to some, it isn’t surprising that, on more than one occasion, he’s managed to get on someone’s bad side.

His behavior has earned him restraining orders from two of his favorite celebrities - Star Trek actor Leonard Nimoy and comic book icon Stan Lee.

One would think that Sheldon would have learned his lesson after these incidents, yet he still doesn’t seem all that eager to change his strange ways.

There’s Nothing Wrong with Him

Fans have long theorized about Sheldon’s inner workings, and many have surmised that he suffers from some sort of mental condition that impairs his social skills. Some believe that he has Aspergers, while others postulate that he has a form of autism. However, series creators have gone on record, claiming that they don’t imagine there to be any diagnosable reason for Sheldon’s behavior.

He apparently suffers from none of the issues that fans have theorized, and it seems like the only logical explanation for his behavior is that he simply adheres to his peculiarities of his own fruition. Fortunately, his friends often exhibit saint-like patience with him, which has helped to keep his social circle in tact after all of these years.

Never Mentioning Tam

As previously mentioned, The Big Bang Theory has been one for quite some time at this point. With 255 episodes and counting, it's fair to assume that we’ve learned practically everything there is to know about Sheldon, Leonard, Penny, and the gang (apart from Penny’s former surname).

With that in mind, it seems odd that Sheldon, having divulged much of his childhood at this point, never made mention of Tam, Sheldon’s young rocket science friend from Young Sheldon. The character was almost certainly created long after Sheldon’s backstory was thought to be set in stone, which is likely why he is never mentioned. It still seems odd that he would choose to omit such a major part of his childhood, though we may get a reason for this in future TBBT episodes.

His Donation

Though Sheldon seems to be pretty set in his ways, his weird idiosyncrasies and intense hatred for physical weren’t always as apparent as they would become in later episodes of the show. Plus, he both does and claims to have done things that would normally be wildy outside of his comfort zone.

For instance, one of the introductory scenes in the show’s pilot sees Sheldon and Howard attempting to make a donation to an adult fertility depository intended for high IQ individuals.

Sheldon’s intent was to spread his apparently superior genetics without the requisite intimate engagements, though he doesn’t actually go through with it. It’s played up for laughs, but this certainly isn’t something Sheldon would normally do.

He Doesn't Always Knock

Every fan of The Big Bang Theory will know that Sheldon is very careful to knock before entering someone else’s apartment. While courteous, his caution quickly becomes annoying thanks to the fact that he’ll stand there knocking on the door in triplicate while repeating the resident’s name until they answer.

While this is generally thought to be something that he’s always done, he can very clearly be seen ditching this ritual in the fifth episode of the first season. It has been said that Sheldon first adopted this practice during an unfortunate run in with his parents as a child, but, at least for a short time, he seems to have lapsed into his old ways.

His Inability To Understand Sarcasm

Despite his vast knowledge of subjects far beyond the bounds of ordinary persons, Sheldon seems to lack the capacity to understand sarcasm. Though he can usually get by, his attempts at such social cues are amateurish at best. His friends frequently point fun at the fact that he tends to take things much too literally, and he’s often keen to point out the technical impossibility of many a sarcastic remark.

However, he manages sarcasm relatively well at several points in the first season, and his sense of humor seems to be much more well-attuned when compared to the social dumbskull he would eventually become. It seems odd that his meager social skills would actually devolve with time, though nobody quite knows just how Sheldon’s brain functions to begin with.

His Strict Flag Rules

Sheldon’s love of flags is perhaps eclipsed only by his love of trains, and he has gone so far as to host a flag-centric video series titled “Fun with Flags” online, as well as instituting a flag for the apartment in which he and Leonard live. It depicts, in his own words, “a golden lion rampant on a field of azure.” He also demands that Leonard never fly the flag upside down unless the apartment is, for whatever reason, in distress. Later in the episode, as Leonard and his pals scramble to get rid of a science experiment on the verge of going wrong, Sheldon flips the flag upside down.

However, the apartment flag can be seen flying upside down at several other points throughout the series.

While the reason for this is sometimes relatively obvious, there are a few occasions on which the audiences is never totally sure of the reason for the apartment's distress.

His Vanishing Brother

Sheldon brings up his Texas-based mother and sister quite often throughout the course of the show, and both even make brief appearances from time to time. Sheldon’s mother always seems to be there when her son is upset, and there was a memorable episode regarding Leonard’s ill-advised romantic interest in Missy, Sheldon’s sister.

That said, it took him eleven season to ever mention of his brother, who, in the twenty third episode of that season, he and Leonard meet in his tire store in Texas. The two argue over the fact that they haven’t spoken to one another in around ten years, and George — Sheldon’s brother — still seems to hold a good deal of contempt for his sibling. That said, it doesn’t make sense that it took him nearly a decade to even make mention of the fact that he had a brother.

He Plays With His Food

Sheldon, as with literally everything else in his life, likes to adhere to a strict set of weird, self-ordained rules. His peculiar diet is often brought up during the gang’s frequent visits to the Cheesecake Factory, much to the ire of Penny. Yet, his mealtime quirks don’t seem to manifest themselves quite as often in the University cafeteria.

The actors aren’t actually supposed to be eating when they film these scenes — that could be just a little gross — but Sheldon really seems out of character during these moments. More often than not, he sort of plays with his food or manipulates it in a way that makes it appear like he actually is eating it. The bottom line here, though, is that the prestigious Dr. Sheldon Cooper shouldn’t be playing with his food.

His Dedication To Apple... And Android?

Observant fans will doubtlessly be aware that Apple devices are Sheldon Cooper’s mobile product of choice, and he can be seen using Apple iPhones and iPads at various points throughout the show’s eleven seasons. While his apparent love for the company seemingly doesn’t spill over to laptops — Sheldon seems to prefer Alienware computers — he seems to remain constantly faithful to the same mobile phone manufacturer.

However, in certain episodes, a model of the green robot — the mascot for the competing android mobile operating system — can be seen sitting on his home desk.

This was more than likely a slight oversight by a set designer looking to cram his desk with all sorts of nerdy paraphernalia, but it seems like a strange thing for Sheldon to have.