Here are some prime examples of how not to react to people in costumes.
When a fan dresses in a stunning cosplay of a character they love, it can be so visually arresting that you'll stop dead in your tracks. And that makes absolute sense, because part of going to cons means getting to see some amazing DIY costumes from the most dedicated fans in the world.
But there are some things you should not say (or do) to cosplayers, regardless of how they are dressed. Buzzfeed gathered together a host of cosplayers and asked them one, simple question -- "What's the creepiest thing someone's said to you while cosplaying?" They wrote the results on a sheet of paper and had a photo taken of them (in cosplay, naturally) along with what they'd written.