During a conversation one character says "I'm only human" in response to being caught in some immoral behavior.
The other responds: "How come people only say that when they do something bad? You never hear people say 'I'm only human' after they run out of a burning building carrying a child they've saved."
Update: Here's the actual quote, which is on IMDB's web site (link above):
Pearl Madison: I'm only human, man.
Leland: It's funny how people only say that after they do something bad. I mean, you never hear someone say, "I'm only human" after they rescue a kid from a burning building.