new york city nyc david letterman Matt Damon boston

Matt Damon stopped by The Late Show With David Letterman on Wednesday evening, and before slipping into a suit and tie, the 42-year-old actor posed for photos in a Boston Celtics tee. Take that, Lakers fans!

Matt is currently promoting his new sci fi action flick Elysium, in which he plays a factory worker who takes on a mission to hijack his way onto a man-made space habitat. So how did he get into such amazing shape for the role?

"It was really hard because I love to eat and drink!" Damon told People on Tuesday at a screening. "It's very hard to motivate me to get in shape." What did his wife think of his ripped physique? "I think she likes the variety," he said with a laugh. "When I did The Informant, I put on 40 lbs. and I was like, 'You kind of like this guy too?' I'm trying to talk her into [liking] that guy because that's the guy I'm most comfortable being."

Um, don't get too happy with the extra weight Matty!