My Ex kept asking to pee between my legs. What does this mean?

What the title says. I was with my Ex for about 2 or so years. I was sitting with my boyfriend tonight and talking and I all of the sudden remembered that he used to ask me that. My BF told me that means he wanted to pee on me. Like sexually.
I am astounded because he was the most vanilla person ever, self-proclaimed. The idea that HE would want to do that boggles my mind, but my BF is insistent.
Info that might be useful: (?)
He would ask a lot, maybe once every two weeks or so?? Very consistent over the time period, but infrequent enough that I never noticed to think into it until now. It was always a joke he would say in a sing-song silly voice and I always laughed it off and moved on.
I’m questioning everything right now though, please help.