The design appears to be a photo illustration of a picture of local ska-punk outfit Informant's drummer, Fat Tim. The picture apparently captures him mid-vomit, which makes sense -- the show is a 21st birthday party for the dude. I just sent a message to the band asking about the artist and will update when I find out.
Update: Fat Tim let us know that Alex Poulos, of the bill's bluegrass-punk (you read that right) band Hats and Statues, designed the poster. And yes, the photo on which it's based really is Fat Tim vomiting. Writes Tim, "yes, that actually is a real picture of me! i went on tour with this one man band called the emotron, and he likes to make videos of people drinking yoohoo until they vomit. i have been in 2 of them." OK, one I can understand. But to agree to be in two Yoohoo puke videos? That's just weird. But they're actually pretty funny. Both are music videos for Bomb The Music Industry songs, "Side Projects Are Never Successful" and "All Alone In My Lonely Apartment." Here are links to the videos if you're into that kind of thing: Side Projects. All Alone.