1. To criticize, exploit, insult, or fail to help one who is in a trusting or vulnerable position. Can Jeff's employee review wait until next week? His girlfriend just left him, and I don't want to kick him in the teeth. After telling us we'd lost our Christmas bonuses, the company kicked us in the teeth by saying we'd be expected to work Christmas Eve.

2. To deliver a humiliating disappointment or setback to one. Losing to our cross-town rivals because of such a terrible call by the ref really kicked us in the teeth.