We have two from our Earthdawn campaign.
1. "Hit him with the flat of the lightsaber"
One of our former players was playing, essentially, a Jedi Knight (don't ask). He had a 'lightsaber', which was actually a magical energy sword, but everyone just called it a lightsaber. At one point, his character was getting in trouble because he kept killing his opponents. So we get into combat, and he declares a subdual attack.
"How?" asks the GM. "You're using a lightsaber."
"I hit him with the flat of the lightsaber," he replied.
We all had a good laugh over that. Now we use the phrase all the time to refer to doing subdual attacks.
2. "Rock to hole vision"
At one point, all of the characters in the group has some form of astral sight (vision that allows you to see into the astral plane, useful for detecting magic and such in Earthdawn), either as a natural ability, or through talents, or magical items. Everyone except one character, an elven archer. We were in a wilderness area looking for the lair of some lizardmen-types, when we come across a large boulder. One of the characters with natural astral vision rolls well enough to break the illusion, and sees that the boulder hides a small cave. He alerts us, and immediately the rest of the party begins to activate their abilities, until all of us can see the cave - except, of course, our poor archer. We tell him repeatedly that there's a cave there, he insists its a rock. Finally, the player turns to the GM and says:
"I try to look at the boulder with rock-to-hole vision."
We now refer to all astral sight as "rock-to-hole vision."
3. "Rock farming"
Refers to the pursuits of anyone of dubious intellect. Another reference to our Jedi player, who left the game. He wasn't always the brightest; at one point, he'd been snatched up by a griffin, and was 400-500 feet in the air. He couldn't understand why it was a bad idea to choke the griffin into unconsciousness - he thought it was clever because he wasn't going to kill the beast with his powers, avoiding the corruption that had been plaguing him. Needless to say, he soon learned that there is a force more powerful than the Light Side or the Dark Side... gravity.
When the player left and the character retired, we decided that he'd gone home to take up rock farming.
4. "Overt operative"
I brought this one up running a game of Dragonstar. I believe one of the characters had just made a particularly poor showing of some Move Silently rolls, so we decided this was his new prestige class. It's the opposite of a covert operative; everything he does is blatantly obvious and loudly announced in a sing-song voice: "I'm opening the lock!" "I'm stealing the files!" "I'm going to assassinate your leader!" It hasn't quite hit common usage yet, but I like it, so I'm going to keep using it.
5. "Plan: Get 'em"
Refers to the usual adventurer tactics of charging a foe, any foe, head on and all at once. Vague reference to the movie Ghostbusters: "That was your plan, Ray? Get her?" And used disparagingly by those characters who would like to see their companions use a little more forethought. It started as a complaint about the Tactics skill in Earthdawn, which gives a bonus to attacks if a plan is followed. Unfortunately, the skill doesn't specify it has to be a good plan, so "Get 'em!" still works.