Ass slapping on itself is not frowned upon, but slapping asses as the vice president is slightly failRP, but not enough for a punishment. Also doing a /me slaps ass doesn't count as rape RP either, so it's allowed in moderation and as long as it's not failRP and it's kept in-character.

Also since you mentioned powergaming, it's not quite powergaming either. If it was like /me slaps ass so hard he cannot walk properly, it would count as powergaming then, as it forces the RP in a certain direction, unlike normal ass slapping. Though of course, it could be like /me tries to slap his ass as it doesn't really change the direction of the RP that much.

But as I said, slightly failRPish, but it's not really worthy of a punishment.