bad spot with KK

UTG is unknown but everyone else is loose, and the button is 55/15 after 150 hands. I wish I had better reads but I was trying multitabling for a bonus.

How would you play this???

Poker Room skin
No Limit Holdem Ring game
Blinds: $0.50/$1
5 players
Converter

Stack sizes:
UTG: $100.00
hero: $260.45
Button: $102.20
SB: $132.20
BB: $99.60

Pre-flop: (5 players) hero is CO with K:diamond: K:club:
UTG (poster) checks, hero raises to $6, Button calls, SB folds, BB calls, UTG calls.

Flop: 5:spade: 6:club: 8:club: ($24.5, 4 players)
BB checks, UTG bets $5, hero raises to $20, Button calls, BB folds, UTG calls.

Turn: 9:spade: ($84.5, 3 players)
UTG checks, hero checks, Button checks.

River: 6:diamond: ($84.5, 3 players)
UTG checks, hero bets $25, Button raises all-in $76.2, UTG folds, hero calls.

My thought with the weak ass river bet was to get value from a worse pair, but also possibly induce a bluff from a missed flush draw or pay off 7x. I figured a set would have played the flop a little stronger...but still wasn't sure.

Results:
Final pot: $236.9

So what are you beating here...?

You're not beating much there besides a bluff, and I don't think that's very likely in this spot. Be careful of talking yourself into calling by thinking you're inducing a bluff here.

I do that too much. People play really weird at this site so sometimes I'm right but yea - not really a good +ev type play/call most likely.

so...can anybody plz suggest a better way to play this? maybe check the river and only call a small bet? raise flop more?