A person you fuck, but only at parties. This can either be agreed upon or just repeatedly happen unplanned. Similar to a fuck buddy
1. Louise: Hey Jim... that party was great. You wanna meet up again sometime soon?
Jim: Nah, you were just a party fuck.
2. Elmo: If this party isn't going great later on, I'll be your party fuck.
Hayley: Yeh ok, I'll come find you if I'm bored.