Acerbic talk is sharp like a sour taste. The criticism is clever — there is wit in it — but it is meant to sting. Reviewers, columnists, and some comedians get called acerbic. It is a grown-up, slightly bookish word; in the classroom, students would more often say mean, sharp, or sarcastic. Though actually, it started as a word for bitter flavour, from Latin acerbus (“sour, bitter”), and people still sometimes use it that way. The sense you will meet most is the clever-cruel one: not just unkind, but unkind with style.