What could he have here? Min raise on the flop could be flush draw, TPGK, two pair or a low set. Since you have 42, a set is unlikely. The only hands I can think of that beat you are K4s or K2s. I can't imagine the 6 helped him and this overbet looks like he really doesn't want a call. In the heat of battle I probably fold, but thinking it over, I think he has KhTh or something like that.

edit: I guess he could have 53s if he's really loose pre-flop and is pushing because he's afraid of the flush. Tough decision.