Question

You could have indicated frankly what you thought was wrong without embittering them with such

Answer 1

You could have indicated frankly what you thought was wrong without embittering them with such vitriolic.

Answer 2

I believe the answer is: vitrolic

Vitrolic refers to a form of criticism that being done with malicious intend. The best type of criticism is the constructive criticism, which being done with the purpose of making other become better. Vitrolic only aimed to create an emotional damage toward the target.