This is a good way to get an autograph from an admired one. Affectionate sex is groovy. A good way to share the room rent, some people think. Nothing interferes with friendship like sex, and nothing interferes with sex like friendship. Intimate sex is wow.
Sexual fluids make a good cement, and they also produce babies.
This was from the section on Classifying Relationships. Consequently, I won't touch it. Ok, after long searching I turned up this pretty good mini-essay on the subject, which is meant to explain things to the gals. Closely related to this is another variety, which I don't really have a good term for. Attempting to jump-start a relationship in this fashion frequently backfires, as the man may intuitively sense what's up, namely that sex is being used as an emotional weapon, and consequently remain at a safe distance.