A made up celebration. No such holiday has ever been organized. It's considered a meme on the internet that is mostly used by trolls, hackers, bigots. They would sometime relate the celebration to homosexuals despite 9/11 has nothing to do with any sexual orientation. They just use it to annoy and offend people.
You'll might see it on Youtube comments:
@Kidstylz
UR GAY
Tr0ll4lif3
@Tr0ll4lif3
Fuck you, dipshit!!!
Kidstylz
@Kidstylz
Gays love going to a 9/11 party
Tr0ll4lif3
@Tr0ll4lif3
WTF???
Kidstylz
4👍 9👎