An idea, thought, or concept that first comes to you when you are taking your morning shower or doing some other part of your morning routine.
Often an epiphany
Often sudden
Often marked by the inability to recall later

Cool thoughts that people think of in the shower. Like "the only time incorrectly isn't spelled incorrectly is if it's spelled incorrectly." :)

Shower thought- A thought that people think of but is more like a question

A wired or unusual thought or feeling you have while in the shower.