Before you try and figure it out, the dudes are dressed as "ceiling fans." (via)

Reddit user Brettera explained that her boyfriend and his roommate decided to wear a couples costume for Halloween, leaving her to fend for herself (though it's not like "ceiling fans" couldn't be a threesome costume, but perhaps that gets weird). So she came up with the perfect costume for the odd girl out: The Third Wheel. 

Not only did this costume give her a clever look for a night of tagging along, but she quickly discovered the wonderful photobombing potential the costume affords.

Sources: Redditor Brettera