I muck it. I think he's getting tricky with one of the two hands that have you crushed. That assumes he was counting on someone raising it up.
How had the pots been forming pre-flop at the table? That is, if everyone is limp/calling then I think he's less likely to have K/K+ as he won't want to be up against 4 players. But if he feels that he can rely on someone (especially you) on making an isolation bet there, then he's probably got the goods.
And if the guy is taggy, I assume he's not in the habit of limping in, which just smells like a trap when he does so UTG. Best case scenario he has a middle PP, but I think you're screwed most of the time.
I don't think showing cards does a whole lot to give you a solid image, as people just assume that not showing means it was a bluff. I mean it helps some, just very little. Now, showing bluffs, people will remember and will make a bigger impression. Just my opinion. I don't have a anything to back it up.