1) "Infamy! Infamy! They've all got it in for me!" - Kenneth Williams (Julius Caesar) Carry On Cleo (1964)
2) "He's not the messiah, he's a very naughty boy." - Terry Jones (Brian's Mum) Life Of Brian (1979)
3) Robert Hays (Ted Striker): "Surely you can't be serious." Leslie Nielsen (Rumack): "I am serious... and don't call me Shirley." - Airplane (1980)
4) "Remember you're fighting for this woman's honour, which is probably more than she ever did." - Groucho Marx (Rufus T Firefly) Duck Soup (1933)
5) "Don't knock masturbation, it's sex with someone I love." - Woody Allen, (Alvy Singer) Annie Hall (1977)
I've seen all but Annie Hall, which is a little disappointing to me. I'd rather think there are a billion amazing one-liners I have yet to hear.
Groucho certainly had some amazing ones... "Last night I shot an elephant in my pajamas. How he got in my pajamas- I don't know!"
Or Mae West... "Goodness, what diamonds!" "Goodness had nothin' to do with it..." Okay, not a ONE liner because you need the context... She's got a squillion more funny ones too.
I'm sure some real great ones will come to me after I post this.