It's okay to be flippant

Depending on what the meaning of flippant is.

Merriam-Webster tells the story of this word:

"Flippant" did something of a flip-flop shortly after it appeared in English in the late 16th  century. The word was probably created from the verb "flip," which in turn may have originated as an imitation of the sound of something flipping. The earliest senses of the adjective were "nimble" and "limber." One could be flippant not only on one's feet, but also in speech—that is, someone "flippant" might have a capacity for easy, flowing speech. Such flippancy was considered a good thing at first.

But people who speak freely and easily can sometimes seem too talkative, and even impertinent. By the end of the 18th century, the positive sense of "flippant" had slipped from use, and the "disrespectful" sense had taken its place.

So the rule is: be flippant but don't be flippant.