Wiktionary
n. (context idiomatic English) A humiliating insult or instance of bad treatment, especially when one is expecting friendship or in need of support; a sudden and unexpected setback; a strong rebuff.
Usage examples of "kick in the teeth".
He'd never expected to come across that in the United States, but here it was, like a kick in the teeth.
He'd known that, but having his superior come right out and say it made it feel as real and immediate as a kick in the teeth.
It couldn't have stopped me if I used my power to force my way in, but it felt strong enough to give me a solid kick in the teeth if I tried it physically.
They weren't in good physical shape for gymnastics, and besides, they would know that men indulging in such stunts could be defeated temporarily by nothing more complicated than a kick in the teeth.