My original crotch rope instructions got deleted as it had nipples in, but here’s another nice way of doing it. It’s good to use proper bondage rope but you can also try it with paracord which is much cheaper and easy to get in big stores.
Even if you follow the first three steps above and tie it off in a bow then you have a very simple crotch rope that you can wear over, or under, or instead of underwear. And if you keep it simple and just single or double strand you could even do it with long boot laces.