Stalled (2013)

During an office Christmas party, the janitor heads into the women’s bathroom to fix the fan.  While he’s in a stall, two women enter and he’s afraid to come out.  He listens to them trash talk about another woman and about the charity auction where they’ll wear bikinis to try to get the highest bids.

When one woman turns into a zombie and bites the other, he realizes he’s trapped.  Soon more zombies have stumbled into the restroom and they can’t figure out how to get out because the door opens in. 

Almost all of the movie takes place in the bathroom and is mostly one man and zombies. There does turn out to be someone else in another stall but we just hear her voice and her face is never shown. This probably would have made a better short film. It’s a horror comedy but not really funny or scary.