The Elf Hat is a hat unobtainable in the store in PFS. It's literally just a elf hat.
The hat of the Santa's little helper. No not a Simpsons dog but the furry little elves!
If you have nightmares of elves sneaking into your room at night, don't be afraid! They don't bite. Mostly.
Just check if they are wearing this hat. If they aren't and are wielding a baton with a loot bag, just sleep. All I got to say.