From Lady and the Tiger. Duncan watches Amanda on a highwire and Tess asks "Old friend of yours?"
"Just a bad habit." Duncan replies.
From "Return of Amanda" (I think)
AMANDA: Why don't you trust me?
DUNCAN: Experience.
That is a good one.
I don't know the name of episode but Methos was the focus. He was forced into a figth by aniother immortal who reckoned ol' Methos was a pacifist pushover....
When methos took his head he said " Just because I don't like to fight doesn't mean I don't know how to!"
After Methos takes Silas' head:
"I killed Silas, but I liked Silas."
From "The Stone of Scone" (maybe that wasn't the title, but you should know what I mean).
DUNCAN: You made a bet with Amanda when she needed money...?
FITZ: You think I'm taking advantage?
DUNCAN: I think you're an idiot.