It’s a combination of slay and amen. (So you use it when you agree with someone but gay) but it also says Slay Men which is somethingeveryone in the lgbtq comunity can get behind
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.