Thumb your nose at somebody/something
Definition 1 of 1
Pro Tip 1/3Visual Gesture
Originally, physically gesturing by placing a thumb on the nose. Now, used figuratively. 
Mocking his rival, he said, 'I thumb my nose at your threats!' with a defiant look.
Pro Tip 2/3Informal Use
The phrase is informal and could be rude if used in serious or respectful contexts. 
She thumbed her nose at the dress code, arriving in casual attire.
Pro Tip 3/3Figurative Speech
'Thumb your nose at' is not taken literally; it means generally disregarding with contempt. 
He thumbed his nose at the curfew, staying out late without care.