LOL. I know this is a weird question, but my two year-old gets upset when I wont use his potty seat attachment when I'm using the bathroom. We have an open door policy cuz we want him to learn and ...
Your son wants you to do as you say and do as he does. The idea of you using his potty seat is entirely up to you. I would suggest an alternative, though, to the open door policy. It's really NOT normal to use the bathroom with the door open, so maybe teaching normalized situations such as HOW a man uses the bathroom, how a girl/woman uses the bathroom and finally how a big boy like him uses the bathroom(WITH his seat) works. He won't see ONE way as being the only RIGHT way.