facetious

Treating serious issues with (often deliberately) inappropriate humour; flippant.

Robbie's joke about Heather's appearance was just him being facetious.

Troutbeck is a tiny village midway between Penrith and Keswick in a very sparsely populated part of Cumberland, and it used to be said by facetious travellers that the reason why it ever had a station at all was to give the engine a rest after it had struggled up the long and trying incline from Threlkeld.

Pleasantly humorous; jocular.

humorously silly or counterproductive for the purpose of sarcastically advocating the opposite.