not serious about a serious subject, in an attempt to be funny or to appear clever

a flippant remark/attitude 轻率的言论／态度

It's easy to be flippant, but we have a serious problem to deal with here. 油嘴滑舌容易，但我们有正经问题要解决。

I think she just thought I was being flippant. 我想她只是认为我态度轻率。