I would probably fold in that situation. At such small stakes, overbets are uncommon, so I'd question what hand he has that would make him bet so much. His hand is likely something like a missed draw, middle pair, or Queen-Ten suited - hoping you'll call with a weaker hand. Unless he frequently makes large bets light, I'd fold. You're getting poor value for your money by calling, probably against two pair or more. While hitting your flush is possible, he could have a full house too. Without good reads on his style, I say let his overbet go and wait for a flush on another hand. Sometimes the best move is no move - save your money for a better opportunity.