What I meant regarding great movie insults was the cleverness of the insult. I realize I didn't make that clear, but anyone can string together curses or racial epithets. To do so subtly takes real skill.
Since you mention Gran Torino, wasn't it obvious that, except for the gang members, Kowalski's slurs were not really meant to hurt others? He was just portraying a behind-the-times, old-school working stiff. After all, he sacrificed his life to provide a future for his Hmong friend. It seems obvious to me that Clint Eastwood is trying to atone for his past portrayals of violent characters with his recent movies. For christ's sake, he cried in Million Dollar Baby.