An abbreviation for "fake mets fan" or "fake jets fan."
This term is usually used when a fan to either the mets or the jets does something un-fan-like such as not knowing a player, not knowing a team fact or missing a game, etc...
"Yoni, your such a fets fan. How could you have missed that game?"
"How do you not know who the running back is Elliot? Your such a fets fan."
When you lookup FetSwing the search results shows the term is gaining popularity and used in mainstream, and adult content.
FetSwinger is utilized term for plural.
Did you hear about the Fetswing party, February 29, 2020?