1. Someone you can tolerate 75% of the time but who, the other 25% of the time, reminds you why you aren't dating or married.
2. A person who's more than a friend but less than significant other.
3. A relationship that's not a relationship.
"I'm taking my 75/25 to my cousin's wedding. I hope she doesn't get any ideas."
"This weekend? I don't know . . . maybe I'll see the 75/25 if I can stand it."
"No way could I live with the 75/25. I'd rip out his throat within a week."
"She's not my girlfriend; we just have a 75/25."