1. To protrude one's tongue out of one's mouth in someone's direction in a childishly mocking, contemptuous, or defiant manner. She just stuck her tongue out when I told her to go do the dishes. The children kept sticking their tongues out at each other, then bursting into laughter.

2. By extension, to do something that openly mocks, flouts, or shows contempt for someone or something. The company continues to stick its tongue out at the government by refusing to comply with anti-corruption legislation. You can't just stick your tongue out at the rules like that and expect to get away with it scot-free!