Class Act Definition

noun

One of distinctive and superior quality.

The principal is a class act who has greatly improved the school.

American Heritage

An entity exhibiting high class especially through refinement of demeanor, conscientiousness of behavior, and/or skillfulness in performance; or an exhibition of high class especially of one or more of those types:

Wiktionary

Used sarcastically, a person, entity, event, or action entity exhibiting the opposite of the above characteristics, i.e., boorish, unprincipled, and/or bungling behavior.

Did you hear about Peter's "milk-milk-lemonade" toast to Lois at their wedding reception? After a class act like that, I'm surprised that anyone in the Pewterschmidt family is still speaking to him.

Wiktionary