When to fold AKs?

In reflecting back on the "old" me, I think I'd be all in pre flop and consider this hand a cooler. However, the more recent, "thinking me," is finally able to pick up on the action before it actually happens. I make a "are you the real deal?" raise pre-flop, in position, only to be shut down.

Full Tilt Poker $0.25/$0.50 Pot Limit Hold'em - 9 players - http://www.thehandconverter.com/hands/455194
The Official DeucesCracked.com Hand History Converter

UTG: $44.00 - 15/6
UTG+1: $56.20
UTG+2: $24.50
MP1: $46.00
MP2: $84.20
CO: $18.05
Hero (BTN): $50.00
SB: $33.70
BB: $42.70

Pre Flop: ($0.75) Hero is BTN with Ad Kd
UTG raises to $1.75, 5 folds, Hero raises to $5.50, 1 fold, BB calls $5, UTG raises to $14.50, 1 fold, BB calls $9
- A 15/6 doesn't have a HUGE pre-flop range, particularly from UTG, but he certainly can be raising with TT-QQ, AK. In addition, I'm not happy about the BB's flat. The BB is loose, but not dumb (not smart either, but definitely not dumb). I want to isolate and / or take this sucker down pre-flop. Therefore, I make a 3bet with the expectation that I am, at WORST, 50/50. However, when I get 3x 4bet, I'm positive I'm the sucker here. I think I have to fold all but AA, KK to a 4 bettor who raises 6% of the pre flops, from UTG no less, AND does not have a markedly high 3bet / 4bet percentage (omitted because I don't have the actual number).

I'm still not understanding the BB's flat of a FOUR BET!

Flop: ($34.75) Kh 4c Js (2 players)
BB bets $17.35, UTG raises to $29.50 all in, BB calls $10.85 all in - I could have predicted this from a mile away: AA vs. KK or JJ. UTG has the AA, and he was fairly committed, pre-flop, playing for a 88BB effective stack (BB had $42 to start), with $28.20 behind.

Turn: ($91.15) 8d (2 players - 2 are all in)

River: ($91.15) 7s (2 players - 2 are all in)

Final Pot: $91.15
UTG shows As Ac (a pair of Aces) - I don't blame UTG for the play here. I don't think he's getting away from a 50BB raise / push. Perhaps he should be flatting the flop, but the money is going all in either way, with $11 behind after the initial lead.
BB shows 4h 4s (three of a kind, Fours) - Wow. Note taken on this idiot. Who is calling a 4 BET, OUT OF POSITION, for 25+% of his stack, PRE FLOP?!?!??!?! So much for my assessment of this player pre flop...
BB wins $88.15
(Rake: $3.00)