Obsessed with watching me in toilet

[Tjorven64]

My 4 year old is always in the bathroom with me , I cant get no privacy whatsoever and I cant even shower in peace because he opens the door so it gets cold. If I tell him to leave he gets really cross and slams doors loud.
He seems obsessed with watching me do number 1 and 2. His morning was ruined because I was in the loo and he missed watching me peepee. He was crying and saying" I missed mums pee pee !!!" And it was ridiculous...I wonder what the neighbours think ? What can I do please help me with advice