For this past week, I've had this blackish gunk under my right thumbnail.  From where?  Where was this residue coming from?  Such a mystery...

Then, today, I was eating a banana, when BHAM (Yes, I spell BHAM with an "H"), it hit me.  It was from digging my thumb into the peel of the bananas I've been eating at every meal as I hungrily attempted to open them.

And thus, the phrase banana thumb was coined.  It is and will be used to denote any situation in which one cannot comprehend the reason behind some occurrence and is plain mystified.

Example, as a verb:
"Man, that last problem on the physics test...I completely banana thumbed!"

Alternate usage of the term is as a noun, describing any mystery one cannot solve.

Example:
"I read this post on OTR and made no sense.  To this day, it remains a banana thumb."

Trust me, it's gonna be a thing.

Use it today and lead the way to the future!