I voted 'did it once'. I had a gf that one night after fucking awhile she slipped my underwear on, and dared me to put hers on. so I did, my package was just bulging thru, she got a big laugh out of it. she said she wondered what having a cock and balls were like, so she stuffed my socks and her long socks into my underwear, and she paraded around the room, looking in the mirror and giggling. we laughed and fucked some more.
my wife positioned herself over my package back when she had penis envy or cock worship. first with with a healthy chub, and then with a raging hard on. she also wore my underwear and stuffed it with socks. she wondered doesn't it get in the way?? and concluded that if she was a guy she would want to be hung & with big balls like me. I even slipped up behind her in the bathroom, and she "peed" for me. that seemed to really turn her on. she likes being on top any how, and that just set her off that night.