I've lifted these from a post I made to an older thread.
"We have no means to harm you."
Our group of four ran into a rather large band of orcs. My fighter/cleric decided to try to communicate with them rather than immediately start fighting, unfortunately he couldn't speak orc. So I would tell the party's wizard what to say, and he would talk to the orcs. My cleric hoped to bluff them and said, "Tell them that we don't want any trouble, but if they attack us we will be forced to destroy them."
What was the wizard's player's translation? "We have no means to harm you." Apparently this made sense to the player, but the orcs attacked immediately anyway.
Whenever someone says or does something stupid despite the fact they should know better (especially during negotiations) we all say, "We have no means to harm you."
"I cast searing light."
Our priest of Pelor was involved in a tragic accident that crippled his left hand to the point of uselessness, but increased his ability to cast light based spells. As a result, he was constantly casting searing light, and nothing but searing light. Now whenever someone repeats the same action, or uses the same tactics constantly, one of us invariably shouts, "I cast searing light."
This and "I'm praying for my spells" also became euphemisms for pleasuring one's self, and are accompanied with the appropriate hand motions when said.
"Priest of Pelor, know your place!"
The cleric got uppity with the local nobility. The result was the DM cutting off the player in mid-sentence and admonishing him in a stern voice, "Priest of Pelor, know your place!"
I don't know why, but it was hilarious, especially the gobsmacked expression on the player's face. When someone questions the DM, or oversteps certain boundaries, someone usually shouts this at them.
"Hey, did you take an extra slice of pizza? Priest of Pelor, know your place!"
"Mohrg Barrel"
We had a player whose bard had a nasty habit of always trying to loot things first, and at innapropriate times. He once looted a villain's corpse in front of a woman and her small child. They stood there screaming as the stranger who just murdered their would-be killer rifled through the man's pockets. A grief counsler he is not.
So we're in a mine and come across a room full of regular old kobolds (we were 10th level on average) and kill them all. There's nothing in the room aside from a barrel. Of course, the greedy bard makes a dash for the barrel, but the fighter is sick of his snatch tactics and tries to get to the barrel first. The bard beats him to it and he opens the barrel, only to be grappled by the mohrg crouched within. We were all attacking the mohrg trying to save him, but the next player up was our wizard (we have no means to harm you) and he vaporized the bard and the mohrg with a lightning bolt.
We don't refer to it as a barrel with a mohrg in it, or anything like that, it is specifically a mohrg-barrel. Now we sometimes threaten to "crack open or drop a mohrg-barrel on someone.", or something similar.
"Butt-Squeak"
Wizard: Trandorf, get away from the Ettin so I can fireball it.
DM: You don't know his name yet.
Wizard: Hey, butt-squeak or whatever your name is, get away from the ettin!
You had to be there. Ever since this incident transpired, there's a good chance that any NPC, whose name is not yet known, will be referred to as Butt-Squeak.
That wizard was the source of many funny events; witness my sig.