Hey y'all,
Lil_G's theory is correct... At some campuses Greek parties are attended only by Greeks. That's how it was at my school when I was there. We did have the occasional non-Greek girl show up at a fraternity party at times, but usually the only guys in attendance were members of the fraternity (or fraternities) throwing the party.
Just wanted to clarify why some folks might have been confused by the original question.
Greek Love,
Carrie