I'd choose Logan, mainly because I've known him the longest and we get along almost like brothers. We also have a stab at eachother as much as possible
Anyone but saitama could slap me. If I got slapped by One Punch Man.... who knows what might happen. I would totally slap the living crap out of Nimajin cause why not.
I don't slap like a girl who just found out her boyfriend was cheating. I slap like those people that point their hand in a "boi" position before unleashing a powerful backhand. If I had to do it on anyone, it would be either @B4L or @Musical
I would slap Porcupine, but I don't like the idea of having quills in my hand. So I would choose either MichaelAndJello or Nimajin