Sorry for the wall of text and I’m not sure if this is the right flair but…

Friday towards the end of the night at a club (I was quite drunk) this girl approached me and we started chatting and she started holding my hand within minutes of talking to me and was all over me (I didn’t try to escalate, she was escalating so I just went with it). The club is closing and I ask if she wants me to walk her to her car she says yes. So I’m walking her to her car holding her hand, we get close to her car and so I pull her towards me to say goodbye, also try to talk to her and maybe escalate more and literally right when I go to look at her some dude lightly slaps my mouth and I’m like “wtf??” I thought this was just some random person I didn’t even notice he was walking in the same direction or even had any association to this girl but this guy is like “she has a boyfriend”. He must have thought I was going in for a kiss cause he lightly slapped my lip. I was like “did you just touch my fuckin face?” And the guy and her took off walking at a fast pace towards the car lmao he didn’t even turn back around when I confronted him. I struggled for a minute with the thought of “should I knock this dude the fuck out?” because I felt super disrespected and shocked but realized it wasn’t worth it. I’m not sure if this was the boyfriend or like a gay friend because it was a light slap it just caught me very off guard. I’ve hooked up with a lot of girls (I’m 31, consider myself pretty attractive) and never had something like that happen before. I am usually able to read body language and know when to or when to not escalate. Anyone else have an experience like this? I don’t get embarrassed often and don’t have any strange experiences like this and I know I’m overthinking it because my anxiety makes me overthink everything, but the next day I felt a lot of shame and like I did something wrong lol. It’s also hard to remember every single detail because I had drank quite a bit. I know I’ll probably never see this person again and I shouldn’t give a shit about what happened but thinking about the situation gives me anxiety and shame lol. I guess my question is, what is the best way for dealing with that feeling of shame the next day when awkward situations like that happen and what is the best method for truly not giving a fuck about insignificant stuff like that?