adjective
facetious
fuh-SEE-shuhs/fəˈsiːʃəs/
Joking about something that calls for seriousness.
The man's facetious use of the broken chair leg as a scepter annoys his colleague.

Etymology
French facétieux conveyed playful wit. Once often approving, the English word came to suggest a desire to amuse that is intrusive or ill-timed, rather than simply good-humored.
In context
What are you by trade? A weaver. And what do you weave? Lance heads, with your worship’s good leave. You’re facetious with me! You plume yourself on being a wag?
More examples
- Please don't be facetious while we discuss your father's surgery.
- I was being facetious when I suggested paying rent with compliments.
- Her facetious reply turns a serious safety meeting into a joke.
Forms
facetious · more facetious · most facetious
facetiously adverb — In a joking way despite serious circumstances.
facetiousness noun — The quality of joking when seriousness matters.