MP: 50 BB
Hero: 100BB
UTG: 300 BB
HJ: 100BB

UTG raises to 6 BB which has been pretty standard in this game so far. He's super loose/aggressive (he check/shoved into an 80BB stack with JQ on a J66 flop and did another check/shove vs a CO "steal" on a pretty dry board). Anyway, 3 callers, I have Jc4c on BTN and call. SB folds BB calls.

Flop 6c9c4d. BB checks, UTG checks, UTG+1 checks, MP checks, HJ a spewy aggressive old guy makes it 18BB. I figured calling was better than shoving here and flat. BB folds. UTG shoves. MP shoves his 50 BB stack. Old guys fold.

This is a super std call right?

i guess so. i fold pf

Of course. Even if he shows you 999 you should still call

So, the pot is around 50 bb with HJ's bet and hero wants to make it 68 by flatting, leaving himself with only 76 behind? Did hero have a plan for the turn if it blanks and villain shoves?

Hero shouldn't flat HJ. Flatting is horrible in this spot since it leads to too many difficult situations on the turn. Take control of it and shove. Hero probably wins the hand right there. If called, hero gets to see both streets with his draw.

As played, it's a standard call. Pot is around 118 and it's 32 to call. Hero has lots of outs against any made hand and he is ahead of any bigger flush draw with his pair. Even against a set, hero has around 30% equity, and the pot is laying better odds than that.

I think the choice to flat here is the key moment, not calling the re-raise.