A person has a crush on someone of their sex. A person can have a gay crush and still be considered straight.
Billy *likes* his English teacher Mr. Johnson. He has a gay crush on him.
by Papa John's Gas March 21, 2006
Adoring someone famous of the same sex to the point that the person would consider turning gay in order to be with that famous person.
Ryan met his Gay Crush Roger Clemens last week.
by The Aye Dr. June 06, 2007