((Hopefully this isn't a repost, I'm still terrible at searching, I searched for "mask" and didn't find anything))
Normally, the Vile Fumigator's Mask that drops off of the Valentine's Day boss has two unhidable tanks that sit on the players back.
Well, these don't always look good with every set of gear.
However, they can be removed with the barber shop.
First, you go into the barber shop, then you equip the gas mask while sitting in the chair - simple as that!
-Not Client Side, checked a few times
hopefully, it won't get fix'd.
EDIT: Also works with the motorcycle sidecar