What are some subtle hints/dead giveaways that someone is Gay

Don't give me any of your "stereotypes are bullshit" crap, how do you go about discerning whether or not someone is Gay. My gaydar seems functional, but applying it retroactively doesn't help. I have strong indications that people who don't fit stereotypes are gay, how do I get a better read on them without straight up asking if they like dudes?