When you say "tap", do you mean: A) Rapped their knuckles on it as if wanting to be let in via a door. B) Tapped dat ass. C) Stuck a pump and spring-loaded ball valve onto it with the intention of drinking the nectar from within.
?
But in all seriousness, it's not a big deal. They did a (seemingly harmless) thing, your reaction was your own, they felt bad and apologised.
Forget about it. Edit: though if anyone taps my ass they're getting a broken hand for their troubles unless I'm in a jovial mood
Dude, if it's genuinely upsetting you, then you should be upset.
But my anxiety has made me obsess over it and right now I honestly don't know what the normal response would be, I just want people to tell me what they would do in this situation