Fatugender is the feeling that one’s gender doesn’t matter, or is useless. Fatugender can also be a xenogender, where one's gender can only be described through the feeling of uselessness, or it can be a term for any gender that simply just feels useless or unnecessary. People who are fatugender may also identify as fatugirl, fatuboy, fatuenby, etc, or they may just be fatugender.
Someone who identifies as fatugender is not useless, as nobody is truly useless. Being fatugender just means that one's gender is or feels useless, can only be understood in the context of being useless, or embodies the adjective of being useless.
The flag was coined by tumblr user autistic-italy. The colours' meanings are unknown. The emoticon on the flag (¯\_(ツ)_/¯) is colloquially known as a "shruggie," and is put on the flag to represent shrugging, or not knowing the answer to something, hence being "useless."