I have this guitar riff in my head (and at my guitar) that I can't seem to drop. It would be an instrumental piece in 5/8 time.
It's nothing terribly difficult - in fact it's pretty simple and easy to play once you have the rhythm down - and I can't shake it. It's the sort of thing that you just close your eyes, lean back in your chair, and let wash over you.
I had never planned on it being a song; it's just something fun to warm up with.
But my brain says I need to turn it into a full song.