Adventures of the Smacking Baby

So, to add to the multitude of differences between A and L, L has decided to go through a smacking phase. He's 14 months and has recently acquired the habit of slapping people.

The frustrating thing about this (besides the obvious pain of being slapped across the face) is that he's not doing it because he's upset. He'll do it when he's playing and then laugh. He smacks A quite a bit. I've never experienced this, so it's a work in progress what to do.

My plan is to take his hand and firmly say, "no hit." And if that doesn't work, I'm going to dump mayonnaise on him and feed him to the wolves. What do you think? Anyone have a good suggestion on how to deal with this?