protest vote
vote cast in an election to demonstrate dissatisfaction with the choice of candidates or the current political system
en-US/ˈpɹoʊˌtɛst ˈvoʊt/
en-GB/ˈpɹəʊtɛst ˈvəʊt/
vote cast in an election to demonstrate dissatisfaction with the choice of candidates or the current political system