Villain and i have 40$ stack.
ok, I am in EP with , , i limp, villain in the SB raise to 1.75$ i smouth call (the guy is tight so i put him on a big pair or AK)
Flop comes: , , Villain pushes all in !!!!! With what kind of hand would he push? If he has KK why not betting the pot? Call or Fold?

CALL

Instacall. Huge overbet push out of nowhere = megadonk move.

If he did it with KK then note that he is THAT kind of megadonk, and move on.

But if he's tight I would limpraise him preflop and expect him to have a hard time folding.

I would have re-raised preflop, hoping he pops it back and we can get all in at that point. If he folds so be it. At this point, you've put 1.75 into the pot. You said he was tight. Would a tight player make this move? Have you seen him do this move? I chuck it unless you've seen him do it before with a week hand. The reasoning is, if you're folding the best hand this time, then there's no reason a better chance to stack this fool will come along soon. Otherwise, you've saved yourself a stack.

You limped with AA to disguise your hand and get it all in, come what may at the earliest opportunity (barring a horrendous board). Follow through.

You played your hand terribly and got lucky. Moves like that are going to cost you a lot of money in the long run, until you get to much higher stakes you should be shooting for making the standard play 99,9% of the time.

I think you played this fine.
I play preflop the same way sometimes to mix up my game.

But in this game you'll make more money open raising or limp-reraising.