What is appopiate?

Ezekiel is in the middle of potty training. He can go he knows how. He just refuses to do it on his own. You have to be on his case and remind him and tell him to go. He is able to hold it and go on his own he does it ever so often. But there is no consistancy. He has been very focused on underwear and bottoms and things of the sort. He has made up songs about his underwear. One of my favorite is "God bless my underwear my only pair". I believe his sisters made this one up for him. We have been talking to him about what is appropriate and what is not appropriate to talk about and sing about. Today he looked at me and said: "Mommy it is not appopiate". When I asked him what he was talking about he said: "It is not appopiate to talk about underwear and bottoms." I think he finally got it. Now if we could only have such luck with potty training!!