John Wallis said he was warned he'd be fired from Neosho Junior High School if he did not keep his “personal agenda on sexuality” to himself.
Embassies had previously flown the rainbow flag in June in support of LGBTQ Pride Month.
“After seeing the rainbow flag in the window, I’ve had it with this place and have thrown in the towel."
The demonstration is aimed at supporting the queer community "in a way that no one would ever suspect."
"Rainbow Warrior" will hit shelves on the 50th anniversary of the Stonewall uprising.
The group likened it to flying the Confederate flag.