When one unintentionally tags along or goes to an event that one may not be wanted at. One feels like the proverbialfifth wheel and like one is intruding and that one is not wanted. A very awkward situation.
Greg: I ended up going out to eat with Sarah's family last night.
Jeff: Really?
Greg: yeah, the problem it that it was a welcome home dinner for her sister.
Jeff: man, you totally gate crashed their cocktail party.
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Sarah: Greg gate crashed my family's cocktail party!
Georgette: bummer.