Picking off a bluff

[Mercman572]

No current reads (I am on my comp at home, my other PT data is at school) but I think I remember this villain as being a bad LAG. I'm just not buying this turn bet. Thoughts?

Party Poker No-Limit Hold'em, $ BB (6 max, 6 handed) internettexasholdem.com

CO ($69.35)
Button ($130)
SB ($116.05)
BB ($126.45)
Hero ($100)
MP ($76.35)

Preflop: Hero is UTG with K[img]/images/graemlins/club.gif[/img], K[img]/images/graemlins/heart.gif[/img]. SB posts a blind of $0.50.
<font color="#CC3333">Hero raises to $4</font>, <font color="#666666">1 fold</font>, CO calls $4, <font color="#666666">2 folds</font>, BB calls $3.

Flop: ($12.50) 5[img]/images/graemlins/diamond.gif[/img], Q[img]/images/graemlins/club.gif[/img], 7[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(3 players)</font>
BB checks, <font color="#CC3333">Hero bets $12</font>, CO calls $12, BB folds.

Turn: ($36.50) 4[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, CO calls $53.35 (All-In), Hero calls $53.35.

Is it weird/bad that I would've folded this if he bet $20?