cock a snook
To regard someone or something with disrespect. Primarily heard in UK. Don't you cock a snook at my instructions—I'm your superior!
cock a snook at someone
to show or express defiance or scorn at someone. He cocked a snook at the traffic cop and tore up the ticket. The boy cocked a snook at the park attendant and walked on the grass.
cock a ˈsnook at somebody/something
(British English, informal)
1 make a rude gesture by putting your thumb to your nose
2 do or say something that shows your lack of respect for somebody/something, especially when you cannot be punished for this: She cocked a snook at her teachers by going to school with her hair dyed purple.