which includes the number of times I've asked him not to get changed in front of me
I've worked with 2 managers who would cycle in and strip/change in the office while talking to us all - in both their cases it was pure obliviousness, and they were perfectly nice people so I just averted my eyes... it's different when they're arses though isn't it.
I'm one of 4 people in a startup. The (technically) second in command is a total bumwipe, who spent 20 minutes the other day trying to brow beat me into giving him administrator access to a system he has no business administrating (especially when we need him to do his actual job) - I had he kept banging on about how his degree is in engineering, how he managed teams of eight people (eight! What a God! I'm running a team of 8 in another job too... of course they all have teams of their own below them...), I had attempts to pull rank, I had "I don't know what you have against me, but when it comes out, it's ugly", I had passive aggressive, and downright rude comments when I was trying to establish why he needed this access, and what I could do to facilitate that, without opening all the security to him - I maintained professionalism, the closest I got was to say that I was disappointed that he felt it was necessary to talk to me this way.
Now, I know the CEO has my back, but, if this guy keeps trying to assert himself as my boss, I will just quit. and it's not me that will suffer.
Set the line, and if they've crossed it, you just have to start looking for another job, and stuff them, feel no regret, no obligation, just leave.