I watched this so often as a kid, I could quote the entire thing verbatim from start to finish.
Starship Troopers. It doesn't matter what mood I was in, I will be in a better one by the time it finishes. Also makes for excellent background for household chores, once you have the whole film basically memorized.
How the hell have neither Mean Girls or The Princess Bride been posted yet?? Those are, like, the most quotable and fun movies ever.