how quick kids catch on...

2 nights ago, Parker was taking for ever going to the bathroom before bed and I was waiting in his room to tuck him in... i walk in to the bathroom and what do i see...Parker peeing in a little cup. My first reaction was "PARKER WHAT ARE YOU DOING" he said, "mom i saw you do this at the doctors before, so its ok to pee in cups." (i have no choice than to take my kids w/ me to the docs for my monthly check up! I guess that is my fault to what he was doing at our house!) I then had to explain that its only ok when your at the docs and he asks for it and no where else.