1. upset the applecart - Verb
2. upset the applecart - Phrase
upset the applecart (third-person singular simple present upsets the applecart, present participle upsetting the applecart, simple past and past participle upset the applecart)
(idiomatic) To disorganize or spoil something, especially an established arrangement or plan.
Synonyms: cook someone's goose, drive a coach and horses through; see also Thesaurus:spoil, Thesaurus:put a damper on