"And a great white bear appears!" (The GM for the very first encounter said this, catching us all completely off guard, especially considering we were in a modern city at the time. From then on we usually said that when ever GM was deciding what was gonna happen next and taking an unusually long pause.) "Monk Man!" (Another encounter in the middle of an enemy base where, we encounter a deaf, mute monk who we attack and dodges everything we throw at him, to only have him join us and constantly pull of insane acts of dexterity , to which we reply anytime we need something done we shout out the after mentioned phrase.) "I'm an orphan. All my friends and family are dead, I killed them." (This one has to be my favorite, a different group in which I was DMing, one of the PC characters was flirting with a female NPC and was doing well until she asked about his family and he replies with this, no hesitation, realized what he said and tried to save it/ take it back. I did not let him. Now we never let him live down the moment he tried to woo a female with the line "I'm an orphan. All my friends and family are dead, I killed them.") "I take off my pants." (Same PC as the one above, this was the first thing he said and did when we started the campaign. He wanted to see if I really meant it when I said 'you can do whatever you guys want'. To which I instantly created a big buff afro wearing gay black guy, named Tyrone, to appear and become "interested' in him. I then made Tyrone, the leader of the mercenary group they ultimately joined. And again we never let him live it down and used that one action to create several sides stories and plot twists and such, through out the entire campaign also whenever I asked what the PCs wanted to do, someone says "I take off my pants." jokingly. ) I have a bunch of other ones, but some other time.