1. It often starts on a forum like 4chan.
2. Some people, like those users on 4chan, have dummy accounts that look and seem like real activists but are almost definitely trolls.
3. The fake hashtag starts to pick up steam as real and possibly fake accounts start circulating it.
4. People then notice the hashtag and start reacting to it, making it even more noticeable.
5. Then it makes its way to smaller blogs.
6. Which makes the hashtag spread even further.
7. Then it's declared as fake.
8. #EndFathersDay is possibly part of a larger troll campaign called "Operation Lollipop":
9. "Operation Lollipop" is reportedly a network of troll accounts that use fake hashtags to bait real activists.
I was told you are interested in my group's (Codename: Lollipop) ongoing operation against the PoOs (People of Oppression). My group poses as feminists on twitter. We bait other PoOs into agreeing with us as we subtly move them more and more to the extreme. The purpose is to make moderate feminists turned off with the movement, as well as cause infighting within the group. As some of our operatives have been compromised, my commander has given me permission to make some of their conversations on twitter public. We want to let the PoOs know that we have infiltrated them so that they begin to accuse each other of being Lollipop operatives.
You can read more about possibly fake "PoO" accounts on a Return of Kings-associated forum here