Gosh I'm glad I found this thread, for the record my DS (15 months) is exactly the same. I actually got a bit worried after our 12mth MCHN checkup when she asked me if he got upset when I told him off. I don't really tell him off, but when I try he just laughs at me and it becomes a game where he does it over and over while in fits of laughter, at least I know I'm not alone.