The concept--four guys in a bar improvise a conversation in a bar--won't set the world on fire. But if half the tavernous chats I've sat through had been this lively or funny, I'd count myself lucky. The cast handily brandish wicked-hahd accents to convey the Beantown locale, which helps lift this improv beyond the everyday, and they've mastered a trick few improvisers--or alleged conversationalists--seem able to get down: keeping the ball bouncing without hogging it. The night I attended the show it was a short, sharp blast, balancing visits to the intertwined issues of dick size and foreign policy with loftier thoughts on planned obsolescence and diminishing returns. Through 9/2: Fri 8 PM. Town Hall Pub, 3340 N. Halsted, 773-472-4405. $5; 21+.