How would you answer this?

The ex wanted to assert control and demonstrate dominance. By demonstrating dominance over her the ex was hoping to project/establish dominance over them as well.

It's hard to guess at somebody's motives but if he was certified NPD it would likely be to test your limits. It's always about them.

To prove how much control he has over her. It’s a dominance thing.

He wanted to show his friends he had complete control over you

Don't know, how did it work out?

The answer is already in the question

Because they are a narcissist. Control. Showing off. They want to have something to hold over your head. Any number of reasons having to do with the fact they are a narcissist.

He’s a moron ?!🙄

Maybe he's closeted gay and wanted to prove he's straight idk

Weird

What a dick