Green’s Dictionary of Slang

1. an uninvited guest at a party.

1922		DN V 147: Crasher – anyone who goes to parties uninvited.
c.1930		(ref. to 1917) N. Kimball Amer. Madam (1981) 330: I didn’t want party crashers or any of the new rich roughnecks.
1939		Pittsburgh Courier (PA) 3 June 11/1: Party crashers who eat and drink without evening knowing [...] the name of the host.
1949		Dan Burley ‘Back Door Stuff’ 16 Apr. [synd. col.] The crasher hit straight for the bedroom.
1950		New Yorker 9 Dec. 31: His main job after the curtain goes up is handling crashers [W&F].
1997–2000		Da Bomb 🌐 7: Crasher: One who gets uninvited to parties.
2023		(con. 1962) J. Ellroy Enchanters 75: Party crasher Freddy.

2. (UK black/gang) as extension of sense 1, a gang member, esp. in context of attacking a rival.

2017

410 ‘Foolishness’ 🎵 Watch how the crashers step in (mad) / Blacked out, hoodie on, and yes we got those leathers.