This thread is awesome. Here are some that I remember.
Sphinxing: To throw the DM for a loop. From a 2E game my friend was running, I came across a (something or other) that said it had a riddle for me to solve. Being a smartass, I immediately recited the answer to the Sphinx riddle. Not only was that the answer, but the DM was pissed and I had to leave the room so he could come up with another riddle.
Compass: Getting lost. From GURPS. A character in my party was at her uncle's house, which was being attacked. When I got word, I took off at full speed (five levels of Super Flight). The GM gave me a minute of saying "I'm flying as fast as I can!" before asking 'Where are you going?' "Um, to Chammie's uncle's house?" 'But where is that?' "Bollocks." Whenever he left our base, someone had to make sure that my character had his compass with him.
From Pathfinder:
Taco: This is just an all-around description if we don't know exactly what something is. "Does that sword look magical?" 'From here, it looks like a taco. Go check it out.'
"What kind of weapons is he/she/it carrying?" 'He's got a giant ogre hook in one hand, a spear in the other, and he seems to somehow be dual-wielding tacos at the same time.'
Suckle From the Teat of Pain: Yelled by our Barbarian when he rolls maximum damage.
Phoning: Said to any character who rolls poor damage. "Way to phone it in."
Engage the Plot Device: When entering a room with no apparent enemies, someone will ask "Do we see anything that looks like a plot device?" Or sometimes when we've beaten the Unholy Taco and the DM is searching his notes for what comes next, someone will say "And now, engage the plot device." And someone else has to make revving up noises, like an engine.
You can see time: Description for a natural 20 on Perception check. Occasionally, it's 'taste' or 'smell' time.
Fist is a Verb: Said when my Monk rolls maximum damage on Flurry of Blows, which is currently 4d10+4d6 frost damage+12 Strength damage. It's happened twice.
T-Bagged: Originally, this started out as me (the DM) saying "If someone can't show up, that's fine, just let me know. We have the portable hole, so your character will be in the hole until you come back." Somehow, portable holeevolved into 'the sack.' From 'sack,' bag was pretty natural. Since you're 'T'emporarily in the bag, you are 't-bagged.'