Share your instances where bugs/oversights in a game let you cause something funny to happen, whether beneficial to the player or just silly. (Looking for stuff that's presumably unintentional, rather than clearly deliberate cheats / Easter Eggs that happen to be funny, though I suppose that could be fodder for another thread.)
Jazz Jackrabbit 2
In the part where a witch turns you into a frog and you have to get the Princess to kiss you to transform back, there's a split second moment after activating the kiss animation that you still have character control. You can use this to turn yourself around so that it looks like the Princess kisses the frog on the butt instead of on the face.
Crusade (AGT text adventure)
In this game, there are some events that can cause you to break your leg, which means wasting a bunch of turns unable to do most actions while you wait for it to heal. In the AGT version, at least, perhaps because of vagaries of the AGT system, the "broken leg" is handled as an object that's put into your inventory when the injury happens and removed again when it heals. The developer was smart enough to recognize that the player might try to "DROP LEG" and prevent them from doing so, but forgot that "THROW LEG" is also part of the standard AGT command kit and didn't add any special exception to that. So you can break your leg, throw the broken leg out of your inventory, and go about your merry way as if it never happened.
Spear of Destiny: Return to Danger / Ultimate Challenge
It's well-known among the Wolf3D fandom that these mission packs redid the sprites and audio for the enemies, despite them mostly still being the same things as before, but one change in particular leads to some rather funny unintended consequences: the SS officer's "Mein Leben!" death cry was swapped for "Tod fürs Vaterland!" but because the Wolf3D sound code is kind of lousy and tends to cut off the digitized sounds a lot, coupled with the heavily bitcrushed audio files, he semi-frequently sounds as if he's just saying a Homer Simpson "Doh!" when killed.