Warning: Contains SPOILERS for The Mandalorian season 2, episode 6, "Chapter 14: The Tragedy."
Moff Gideon captures Baby Yoda in Baby Yoda, whose real name is Grogu, Gideon was finally able to get his hands on the Child in "The Tragedy," courtesy of his Dark Troopers. Gideon clearly has big plans for Grogu and his extremely high midi-chlorian count, but the episode also teases Baby Yoda's interest in the Darksaber.
The very end of The Mandalorian season 2, episode 6 finds Grogu in a holding cell, where Gideon visits him and he gets to see the Darksaber for the first time. It makes sense that Baby Yoda would be interested in it: beyond just it being a shiny new toy, it also presumably reminds him of the training lightsabers he would have seen (and perhaps even wielded) at the Jedi Temple on Coruscant. However, once Baby Yoda is done Force choking Stormtroopers and is ready for nap-time, Gideon warns him off the Darksaber, urging caution around the weapon.
Gideon tells Baby Yoda: "You're not ready to play with such things. Liable to put an eye out." It's a great, if somewhat sinister gag even amidst the horrible circumstances in which it comes, and it's a joke Star Wars fans have been making about lightsabers ever since 1977. While not actually in the movie, a production still that shows Luke Skywalker pointing his lightsaber at his face, from an alarmingly close range, has long been made a joke of by fans for how dangerous it is, becoming one of the movie's biggest memes in modern day but a gag long before that too. With Gideon's comments in The Mandalorian, then he simply echoes the amusing concerns fans have had for a long time.
While this is the first time Star Wars has brought the much-loved joke into canon, there is also a lot of truth behind the warning too. It's long been evident just how powerful lightsabers are, but Star Wars Rebels showed just how they can literally be used to put an eye out, with Maul blinding Kanan Jarrus with one in the season 2 finale, "Twilight of the Apprentice." Thankfully, his eyesight was eventually restored, but it does make sense why someone - even a villain like Gideon, since he needs Baby Yoda to be fully healthy for now - would make such a warning.
The Mandalorian is no stranger to making old jokes canon, having already referenced things like Bo-Katan still wants to take the Darksaber from him, then there may come a time when Gideon should've heeded his own warning.