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 out her tongue at me when I told her to go do the dishes. The children kept sticking out their tongues 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 out its tongue at the government by refusing to comply with anti-corruption legislation. You can't just stick out your tongue at the rules like that and expect to get away with it scot-free!