1. To bite one excessively, as of insects. If you're out here at dusk, the mosquitos will eat you alive.

2. To overwhelm and/or easily defeat one due to being more aggressive, powerful, etc. Our team isn't very good, and I'm worried that the competition at this level will eat us alive. Lena is so meek, I worry about her moving to the city. They're going to eat her alive.

3. To criticize one harshly. The teacher will eat you alive if you come in without your homework again today.

4. To cause one significant physical or emotional pain. Even though it's been a while, I think memories of that accident are still eating him alive.