"Bubkus" is a variation of "Bubkes" (also spelled "Bupkis"), of Yiddish origin.

It means "nothing at all", as in:

A person who doesn't realize they are transgender yet, or is in denial; an undeveloped transgender person. When they realize, it's referred to as the "egg cracking."

Kind of like saying “that’s trash” or “that’s stupid” You might year your Yiddish grandma yelling “Bubkus” at the tv or at her ex husband. Very useful and honestly funny word, I recommend to use it in every sentence you can.