Probably Mean Girls closely followed by Borat. After that a mixture of Austin Powers and Arnold Schwarnegger quotes, but they're spread across multiple films each. Considering how popular Borat was among my friend group shortly after seeing it, my poor memory might be unfairly thinking it's the second most often quoted by myself. Borat could also easily be seen as cultural appropriation, where as Mean Girls doesn't have that baggage. If we were talking media in general, then South Park. I also went through a phase of quoting Kidulthood a lot.
"You go, Glen Coco" being the quote I used most often a few years back.