spontuneous
A song that gets stuck in your head without prompting. Also, any opportunity to break out randomly into song. Often related to an earworm
I found myself spontuneously humming "Piece by Piece" under my breath.
When I complained that it was "hot in here," my friend spontuneously sang "so take off all your clothes..." UGH!
When I complained that it was "hot in here," my friend spontuneously sang "so take off all your clothes..." UGH!