upset the applecart

upset the applecart или upset one's applecart  {v. phr.},  {informal}

Разрушать планы или какое-либо дело, часто неожиданно или нечаянно; изменять ход или порядок вещей, часто неожиданно; разрушать чей-либо успех или смешивать планы на его достижение.

John upset the other team's applecart by hitting a home run in the last inning and we won the game.

We are planning a surprise party for Bill, so don't let Mary upset the applecart by telling him before the party.

Frank thinks he is going to be the boss, but I'll upset his applecart the first chance I get.

Ср.: ROCK THE BOAT.