William, the 15 year old

William is a 15 year old in a 5 year old's body. He had a play date with his neighbor today, and when I put on the train music from Charles' birthday party yesterday to accompany their engine building craft, William began proclaiming the music "annoying." When a new dong came on, he would again call out, "annoying!" 

Just now, after going inside to get a cup of milk, he came outside with his lidded cup that he found in the fridge. Instead of drinking from the spout of the lid, he drank from the air hole at the back of the lid. I told him not to drink from the tiny hole because it might make a mess. He replied, "Relax. It's fine." Seriously? He told me to relax?!