50nl: KK vs donk minraise

[DLKeeper1]

Villain was nauseatingly terrible. Runs 33/1/0. Really terrible. His minbet is screaming set to me, but I have a lot of trouble letting this go. Thoughts?

Full Tilt Poker
No Limit Holdem Ring game
Blinds: $0.25/$0.50
6 players
Converter

Stack sizes:
UTG: $50.75
UTG+1: $1.90
CO: $26.50
Button: $48.50
Hero: $66.55
BB: $49.50

Pre-flop: (6 players) Hero is SB with K[img]/images/graemlins/spade.gif[/img] K[img]/images/graemlins/heart.gif[/img]
2 folds, CO calls, Button folds, <font color="#cc0000">Hero raises to $2.5</font>, BB folds, CO calls.

Flop: 2[img]/images/graemlins/club.gif[/img] T[img]/images/graemlins/club.gif[/img] 5[img]/images/graemlins/spade.gif[/img] ($5.5, 2 players)
<font color="#cc0000">Hero bets $4</font>, <font color="#cc0000">CO raises to $8</font>

Hero???