1. Literally, to raise one's index and middle finger up at someone or something, with one's hand turned outward (a rude gesture of disrespect in the UK). Primarily heard in UK. It's not uncommon to see young kids sticking two fingers up at police in this part of town.

2. By extension, to demonstrate one's disrespect, dislike, or anger towards someone. Primarily heard in UK. Voters have essentially stuck two fingers up at the political establishment by voting for populist candidates from across the country.