Having sex in a box. Most commenly when a man or woman is homless and living in a box and a someone sees them and they end up making love in his/her box.
"That homless guy is really sexy, I'm going to go have boxsex with him"
"That guy totally just had boxsex with that girl"
When the receiving sexual partner, typically a female, is intentionally put inside a box for sexual purposes. The box is usually shut in such a way that the person inside can't escape without assistance, and there is usually a small air hole and a bigger "Sex Hole" where the vagina/anus is located. A Sex Box is normally used in a situation where a receiving partner wishes to be "used" by multiple people, and the box allows them to both be traded like "property" and allows the person on the outside to "use" him/her without caring about their looks, since all they see is the vagina and/or anus. Some variants include a mouth hole, and more permanent housing.
Guy 1: Where's your girlfriend?
Guy 2: Her and I had box sex last night.
Guy 1: So is she still in the box?
Guy 2: Yeah.
Guy 1: Really? Can I borrow your sex box?
Guy 2: Sure, I don't mind sharing her.
When two people hide in nearby cardboard boxes and masturbate until orgasm
. As seen on Scrubs
Elliot: Were you thinking about me?
Keith: I always think about you during box sex, you know that.
when four people give oral sex to each other in the shape of a square
Chad: "whens the box sex!?"
Michael: "sometime tomite, after you make me a sammich"