Green’s Dictionary of Slang

disgusting, repellent, shocking.

1973		Kohl ‘Note on GROSS OUT’ in AS XXXVIII:1/2 157: That was a real gross-out party.
1987		‘Joe Bob Briggs’ Joe Bob Goes to the Drive-In 177: No gross-out scenes.
1994		J. Wambaugh Finnegan’s Week 103: They didn’t understand the cynicism, and the gross-out gallows humor.
2004		Salen & Zimmerman Rules of Play 443: One by one, players tell a gross-out story, each tale more disgusting.
2010		Sun. Times Mag. 19 Dec. 23/1: many of these are pretty revolting, but this ‘gross-out’ material becomes a shared joke.
2015		Guardian G2 3 July 13/1: Perhaps gross-out horror isn’t the best medium to tackle the endemic racism and brutality in th US penal system.