Watch These Stripped-Down Valentine's Day Runners Try To Beat The Cold ... And Our Celeb Trivia

For a good cause!

When you volunteer for charity, you normally do it with your clothes on -- but Cupid's Undie Run, held in cities throughout the country around Feb. 14 each year, raises millions of dollars by dropping drawers. It's all to help fight a tumor-causing genetic disorder called neurofibromatosis (learn more here), and the event's motto is "put the hilarity in charity!"

This year, we joined along in New York City -- albeit with our winter jackets zipped up -- to keep participants distracted from the freezing temps. MTV's Matt Strickland tested their celeb relationship knowledge, and gave a Valentine's Day rose for each correct answer.

Check out how they did below, although they're all winners for having big hearts and serious cold endurance: