LOL! My daughter did that once. She didn't remove her diaper, though, I'd left her lying in the crib after changing her, and decided to let her go au naturale for a bit...not a good idea.

Apparently, she wasn't 'done' with her bodily functions. I could hear her playing happily in her room, and when I went in to check, she had had quite a bit of fun 'decorating her crib and the wall behind it! She gave me the most beautiful grin as if to say 'Look what I did! Isn't it pretty?' NOT! I didn't punish her, she was just a baby, and I shouldn't have left her without her diaper. And I never did it again. :/