I would probably fold. If you reraise him right there on the flop and he calls, you're probably beat. I'd be very wary of 2-pair or some sort of straight/flush draw combination though. Even if you're ahead not, he might be the favorite, and he's got position on you. I wouldn't be against reraising if he's typically loose, but you'd have to be willing to throw a lot of money into a pot that you're going to be out of position in.