This was a tough one. I am a big fan of quoting movies so it seems impossible to limit it to one. I was able to narrow it down to this one beacuse 1. The Sandlot is one of the greatest movies ever created. and 2. It is the quote that I honestly use on a regular basis.

"You're killin' me smalls!"

Why do I love it? Beacuse sometimes there is no better response to someone being lame.