Too many good ones to pick a favorite. But I love the scene in Kelly's Heroes where Telly Savalas has the squad lined up and is alternately dressing them down and trying to psyche them up about their r-n-r at a run-down farm house in the middle of nowhere.
"...If I hear any more wild talk about going down to Battalion and shooting all the officers and raping the nurses, I'm gonna strangle the guy with my bare hands! Do ya understand that?!"
"Sarge...?"
"Yeah?"
"I think I got the crabs."
Savalas pauses..."We're gonna boil our laundry."
Regards, Shuckins