dad smacks teenage daughters butt?

Every family is different. If the girl is uncomfortable with it she should just say so. If not then mind your own business.

i think its wrong to be honest

I'd believe it but there is nothing wrong with the teenage daughter making a rule that he CAN NOT do that any longer because SHE is uncomfortable with it.

He's likely been smacking his daughter's butt all her life. Out of anger, out of affection, out of habit. And it, more often than not, has nothing to do with "bad" at all. It's been an affectionate swat for a decade and is a habit of exchange. But if the teenage daughter doesn't want it anymore.. SHE makes the rule it no longer happens.

It’s now a boundary issue. He’s obviously not accepting she’s growing older, but it’s now inappropriate.

Smacking how? As a form of discipline or like in a sexual matter?

It depends how often he does it

I reserve judgement on that, until I know if the girl was 13 or 19.

I think dad is a little pervy and needs to keep his hands to himself.