Hat of a masked man...?

where do you get it from? i just saw some1 wearing it...

does it expire?

You can obtain that hat from the Mansion PQ started by the Butler. You can find the Butler in the foyer of the Mansion and he is standing in the middle of that map, above the Maid.
You need a party of 4 people to start the PQ. I think Isaac wrote a guide on how to do it. It's quite simple when you know the basics and also pretty fun :p
The hat expires after a week though )= But you can get a new one ^^ and indeed it looks awsome :p

That quest is also partially glitched, as far as people can tell... Sometimes none of the mirrors drop a mirror piece, meaning you can't keep going to the next map in the PQ