A TRAFFIC tie-up at 40th and Lexington yesterday had an unlikely culprit: Joan Rivers. The comic was en route to a gig in Atlantic City when her stretch limousine sideswiped an MTA bus. “No one was injured,” Rivers tells us. “In fact, the only one who seemed irritated by the whole affair was a tiny Jewish woman who kept saying, ‘I don’t care who is in the limo. I have somewhere to be!’ ” Rivers ended up posing for pictures and signing autographs for the bus passengers.