Guy friend slapped my ass

So a few friends and I were at the bar last night (I wasn't drinking at all because I drove, but everyone else was drinking). I have this friend, we'll call him Joe, and he went with us. Joe is kind of... socially awkward? But he's been a great friend and has always been pretty supportive and fun to hang out with despite his awkwardness.

Anyways, he's been single for about a month or 2 after breaking up with his live in gf (she was pretty mean and demanding from what I could tell) and now Joe has basically turned into a thirsty ass mofo. I've noticed that he's been a little touchy feely with girls lately, including my friend (we'll call her Karen) and me even though we both have boyfriends, both of whom he has met and both of whom go to the bars with us.

Well on this particular night, my bf couldn't make it out to the bars because he had an important meeting in the morning so he wasn't there, but Karen's bf was. Well as we're standing at the bar, I smacked Karen's butt as a funny haha kind of thing, and that's just the friendship dynamic us girls have. Well the Joe says "no that's my job" to which I was like... uh no it really isn't. And his response was to smack MY ass, and I was like wait wtf did he really just...?

So I went off on him saying stuff like "no you don't get to do that", and I was especially cranky since he knows and likes my bf.

When I told my bf he didn't get instantly mad, but he said it will make him more cautious around Joe and he will get pissed if he does it again.

My question is, did I overreact? Did my bf under-react?? And should I have a talk with Joe about this or would me going off on him be sufficient?