When gay people think that someone is gay: usually motivated by subtle interactions that only another gay person would really notice, used as a tool to find other people like us with the intent of feeling less alone and feeling like it’s okay to talk about being gay without fear of violence.

When straight people think that someone is gay: almost entirely motivated by homophobic stereotypes, usually ends with fetishistic behavior, forcing someone out of the closet/outting them to others, or enacting violence, never beneficial or necessary for anything except bragging rights that they have good “gaydar”.