If you couldn't score tix to House of Pain's UFC-sponsored reunion gig at the Roxy tonight, you can still jump around with the group this afternoon over at CONCEPTS in Harvard Square, where HOP will be unveiling -- and signing -- their St. Paddy's Day special-edition Campus 80 Addidas Originals ("Fine Malt Lyrics"!) and matching basketball jerseys . . . a must-have for any serious yah-dood sneaker fiend. There's booze, food, DJs, and giveaways from 3-5 pm at 37 Brattle Street in Cambridge.