I'm copying this straight from my support ticket:
Me: As far as I'm concerned, there is no currently possible way that we can remove the Spiral Bombhead Mask from our arsenals. It can't be unbinded, thus not being able to get traded, and cannot be sold to vendors either. Is there a way I can actually get rid of this item? If not, please make the item "vendor-able" please. :)
Hyperion: Hi! Unless there is an option to "trash" the mask (which will destroy it permanently), there's currently no way to remove it from your arsenal, no. As far as I know, there's no current plan to make them "vendor-able" (good word!), but you may want to make a post along those lines in the Suggestions section of our forum.
So yeah, does everyone else think it's a good idea to be able to remove the mask if they don't want it? It's not a big deal at all, and I'm not exactly ranting, but I just thought it would be a good suggestion to make this game neater, and at the same being easy to implement. It would help make people's Arsenals look neater :)
At the same time I'm also wondering if other Bombhead Masks can be vendored.
You can't sell any of the bombhead masks or Rose stuff.