The best line in a film EVER, well, apart from another which I'll also put here, was in an old black and white gangster film from the forties, it was on TCM or something and the film was full of those kind of phrases. Anyway, they had this bloke on a roof who'd been grassing to the feds and they were asking him to confess and he was giving it all the "I ain't done nothin' Johnny, I wouldn't tell on ya", and Johnny didn't believe him see (they said the word see a lot at the end of every sentence) and he pushed him off the roof and said "he can sing like a canary let's see if he can fly like one". He couldn't.
Second best line in a film is from The Three Amigos.
Her: I was thinking later, you could kiss me on the veranda
Him: no, the lips will be fine.