> The worse part is reading a PR, and catching a reintroduced bug that was fixed a few commit ago. The first time i almost lost my cool at work and said a negative thing to a coworker.

Losing your cool is never a good idea, but this is absolutely a time when you should give negative feedback to that coworker.

Feedback is what reviews are for; in this case, this aspect of the feedback should neither be positive nor neutral.