Joe does that to me, too. Like, a couple of months ago, I had them in the tub, and the power went out. I said "Oh shit!" (thinking about two soapy kids in a tub full of water in the dark) and next thing I know, I hear, "Shit!" It took me forever to get him to stop saying it. But now, if I do slip and say it, he'll go on all day saying it.
He's also talking a lot more every day, and he's really starting to pick up potty-training (FINALLY). I think a major part of that is he finally tells me when he has to go. He hasn't had an accident in six days. Now I just have to get him going in public. And he'll finally wear underwear, as long as he gets to pick them out. I think he's abandoning his nudist ways, at least for the time being.