At 5 yrs old, it's pretty hard to assume that they fully understand the implications of what they are saying. At least he's using the words in context. If he were saying those words in a nasty context then you'd have something to worry about and start wondering about his influences. For now, just blow it off. If he sees that he's getting a reaction from you he'll want to do it more because he thinks he's being funny to everyone.(I know, easier said than done). I agree with whomever said earlier that if you're not getting complaints from his teacher than what he's doing is probably pretty standard for a kid his age. If it gets to a certain point where it's disruptive to the other kids or he's out of control with that language, his teacher will be sure to key you in on it.
For what it's worth, I remember being that age and thinking that those words were funny. It's just a matter of maturity which is hard to expect from a 5 yr old let alone a 40 yr old guy. I don't think that boys ever grow out of thinking that boobs and farting are funny)
As far as touching your boobs, i don't know what to tell you about that. It's funny how much humility your kids teach you, huh? I'm the kind of person who can just laugh things like that off knowing that it doesn't matter what other people think, but if it's a big problem for you, just continue to explain that it's inappropriate. He'll get it eventually.