When someone has anal sex with a woman, then moves down to standard vaginal intercourse.
friends talking to each other "I did the chocolate curtains on Helen the other night"
When you have sexual intercourse with a female who is on her period.
Tom: I had sex with emma when she was on her period
Craig: bloody towers! that must have been messy
A threesome with two guys and a girl, where one guy is getting a blow job and the other is taking the woman her up the anus. The two guys are high-fiving over the girl to make the Blackpool tower shape.
Can you remember that time we did the Blackpool Tower with louise?