A ketchup party is a name given to a young persons swingers party.
Involving most of the people there being drunk. Various activities take place like at regular parties but everyone, seems to kiss one another no matter the gender or relationship status. No sex occurs at these parties but blow jobs and fingering etc may occur (depeding on the state of people being drunk or their eagerness).
the reason for it being called a ketchup party is unknown, but may have referance to the event being saucy
Bill- Hey Loz you got to invite me to a ketchup party, I want to practice my kissing
Loz- But Bill you don't even drink
Bill- Yeah but the girls that go do ^^)