Flippant

Don't be flippant about this.

His response was flippant.

Her flippant attitude won't get her hired.

It was a flippant comment.

Tom made a flippant remark.

I know what it means to have a temper. You’ve seen what I'm like when I lose control. But even at my worst, I'd never willingly kill someone! And if I did, I know I'd feel some serious remorse for it. Even if I'd felt vindicated in the moment, once I calmed down, I'd regret my actions. I would never be so blasé or flippant about taking a human life, and neither should you!

a sort of flippant, vain discourse

The conversations had grown more adult over the years—she was less flippant, at least.

In the mid-1950s we both wrote for the same weekly, where her contributions were a good deal more serious and less flippant than mine.

Our society treats smoking flippantly as a slightly distasteful habit that can injure your health. It is not. It is drug addiction.