Noun:

Gatecrasher,

gatecrashers's Usage Examples:

usually perceived negatively, although more liberal hosts may permit gatecrashers, depending on their behavior.

grew in size, with the number of attendees sometimes being swollen by gatecrashers.

busy focusing on building up an army and reopen the mine to send the gatecrashers away.

made up of two teams from each state, plus three additional teams—the gatecrashers—from New South Wales, Victoria and Western Australia.

dot-com parties included live bands, decorations, product demonstrations, gatecrashers, exotic or fancy venues, excessive alcohol consumption, and "schwag bag".

Soon the truth about Dan is revealed to Ellie's friends; however, when gatecrashers arrive at the party and cause trouble, Dan intervenes and saves the day.

Synonyms:

interloper; unwelcome guest; intruder; crasher; trespasser;

Antonyms:

acquaintance;