Slang term meaning that one is just willing to have sex. It's like having a friend with benefits. Just make sure the participating members are clean and use as much birth control as possible.
Penny was a girl who was always "down to fuck". We had so much fun together. I hope her birth control lasts!
When a person(s) is totally ready to become one with their seating arrangement and engorge themselves with as muchfood as they can possibly stomach. This is abbreviated as DTF.