For me, whenever I heard some variation of "That's so gay!" (as a synonym for "bad" or "lame") in school, it made me flinch and pause because I didn't know if it meant the classmate would shun me if they did find out I'm gay...or if they were just using it casually and carelessly, but actually wouldn't have any problem with being friends with me in the event that my sexuality was confirmed for them.