Opponent (UTG) was 25.5/6/.8 after 418 hands. He was a little loose but I also thought he was passive. He would limp on the button a lot. Whenever I raised from the BB when he limped he would fold.

PokerStars No-Limit Hold'em, $0.50 BB (8 handed) from (Format: Bet The Pot)

saw flop|saw showdown

UTG+1 ($37.65)
Hero ($53.50)
MP2 ($14.25)
CO ($30.45)
Button ($28.25)
SB ($52.15)
BB ($52.90)
UTG ($33.65)

Preflop: Hero is MP1 with , .
UTG raises to $1, 1 fold, Hero raises to $4, 4 folds, BB calls $3.50, UTG raises to $12, Hero calls $8, BB folds.
Should I have just pushed here. I had him tagged as a passive player so I thought he would have to have a really good hand to reraise me. Plus the utg mini raise is sometimes an indicator of a great hand at these levels.

Flop: ($28.25) , , (2 players)
UTG bets $2, Hero calls $2.
Nasty flop. What do you make of the small bets?

Turn: ($32.25) (2 players)
UTG bets $3, Hero calls $3.

River: ($38.25) (2 players)
UTG bets $16.65 (All-In), Hero folds.
Good fold?

Final Pot: $54.90

For a passive post flop player over 400 hands I have a hard time believing he will fire three barrels on AK. The way it played out good fold.
That being said my money would have been all in preflop. If he has AA so be it. He could just as easily have QQ-JJ-AK.

Correction: Actually pretty whimpy barrels...lol posted too quickly.
He might have AK but since you called everything everywhere who knows.

Push preflop.

I think preflop is a fold with your read against a full stack, a push without.

Calling a 4-bet with KK is ugly, you really don't know wtf to do when a Q or A flops other than get own3d.

As played push flop.

A guy who min raises UTG usually has a pair or Axs. When he gets reraised and he re-reraises, hes going to have AA most of the time.

Having said that, I would almsot never fold KK preflop ina a 6 max game especially when the guy only has 2/3 a buy in.

Did anyone even notice that the BB cold called 8BBs? I think that would be the deciding factor for me to reraise all in preflop, but I would expect to see AA alot of the time.