for the result orientated...
If you sit down and really think about this one, he didn't play this badly. I couldn't figure what hand MP had (the flush was unlikely but possible, you get some wacky people, and I was just too new on the table to be sure)., so I checked behind.
He shows 5♠6♠ for two pair.
I show my deuce for the 6-high straight, and take my money.
here's how his hand must have looked:
PF limp for $5, and then 3 players pay $15. He only has to pay $10 for a pot that is already $50 - 5:1 odds
Flop - middle pair. weak betting on the flop, lots of 2nd chances for his hand, call the button bet and see one more (this, I think, was his worst play).
Turn - he now has OESD and FD (although only one end of his straight and none of his flush is good). Figures he has 19 outs (9 FD, 8 OESD, 2 fives), worth calling a 1/2 pot bet.
River - two pair not what he wanted, check again.
knowing this I might have been able to get a little value out of him (bet 1/4 pot or less), but I think the check was the correct play.