Boobies

Lately Matthias has taken to boobies. It's almost like a sign of affection. He likes you, he grabs your boobs. It's funny in the way that I can't believe he's doing this. So I laugh, which only makes him do it more. Yesterday I was giving him a piggy back and his hands went from around my neck to my boobs. He's lucky he's my son or I'd have to kill him (I'm JOKING!!!).

Any advice on how to stop this boobie mongler?