Gay panic

1. When a person experiences a feeling of nervousness or excitement after having an interaction with a person of the same gender they are romantically/sexually attracted to.

2. When someone else finds out about your sexuality without you intending them to.

1. "Omg my crush just spoke to me, I'm having a gay panic moment!"

2. Them:" Wait, she? I thought you're straight "
You: *in gay panic mod*

Gaydar

The ability of a homosexual person to detect if someone else is homosexual as well.
Usually, gay people are able to sense other people's 'gayness', based on their own experiences and observations.

"That guy is so cute!"
"You know he's gay right?"
"Seriously?"
"Yeah, my gaydar goes off majorly when he's around"