Favourite gaming glitches you've found throughout the years

what is your favourite gaming glitch,and how do you do it?                            

the decor noclip glitch in this game. basically, just drift in to a decor when you're behind it. but don't drift when you're far away from the decor, only when you're very close to it. i think it has something to do with the collisions but i'm not sure

In this MKPC, if you hug into the wall, you’ll clip through wall, even if the wall height is 100ft high, you’ll still clip through, but only if it polygon shaped, rectangular and square shapes won’t work, that’s my favorite glitch.

The Rare Endangered Spy Crab

I know Valve tolerates it, but I doubt they would have purposefully built that in to the game.