As a noun fanny
is (british|irish|australia|nz|south african|vulgar) the female genitalia or fanny
can be (uk|naval slang) mess kettle or cooking pot.
As an adjective facetious is
treating serious issues with deliberately inappropriate humour; flippant.
(en proper noun
* 1883 , Heart and Science , Chatto and Windus, page 227:
- "My name is Frances. Don't call me Fanny'!" "Why not?" "Because it's too absurd to be endured! What does the mere sound of ' Fanny suggest? A flirting dancing creature - plump and fair, and playful and pretty!"
Treating serious issues with deliberately inappropriate humour; flippant.
Pleasantly humorous, jocular.
- Robbie's joke about Heather's picture was just him being facetious .
* See also