flippant

[Francois]

not serious about a serious subject, in an attempt to be amusing or to appear clever:
a flippant remark/attitude
It's easy to be flippant, but we have a serious problem to deal with here.
I think she just thought I was being flippant.

Is it common? Are there "better" alternatives?

FRC

 

[twostep]

You may hear "off remark" in the US.

 

[MikeNewYork]

not serious about a serious subject, in an attempt to be amusing or to appear clever:
a flippant remark/attitude
It's easy to be flippant, but we have a serious problem to deal with here.
I think she just thought I was being flippant.

Is it common? Are there "better" alternatives?

FRC

I wouldn't call it common, but it isn't a rare word. There are many possibilities here:

http://thesaurus.reference.com/search?q=flippant