OMG - my Gaydar is non-existent! I'm generally clueless about other people in groups.
Case in point:
In 2014, I attended a party - a mixed party: gay/straight, male/female, old/young - and there were about 50-70 people there. I was still at the end of a 4-year marathon divorce process, but i was "livin the single life" and made it clear to several people at the party that I was "available"... Nonetheless, I went home alone 
2 days later, I got a text from an unknown number. This guy says we met at the party, and that another person there gave him my number. He wanted to have dinner. I wasn't sure WHO this guy was, but there was this dreamy 55 y/o guy there I had had my eye on. He too had kids, but he was financially well off and retired... (I was struggling financially because of the divorce). He was looking forward to traveling and "enjoying his life to the fullest"! Anyway, we had chatted briefly, but he had "moved on" and started chatting up a group of very young guys... message received.
But, now I wasn't so sure! The thing was: I was certain his name was Richard, and the caller's name was David. But, I'm awful with names, so I went on the date.
Instead of 55 y/o Richard, this beautiful 26 y/o ebony God sits down at the table, says HE is David, and he was so glad I agreed to see him. Well, I did NOT go home alone that night...
David, being much younger, was still a very active "socialite" in the scene of Tampa Bay's Gay Life... we were invited to parties, and David liked to go out dancing (I'm an absolutely horrid dancer!)... On MOST nights, David would point out guys who HE SAID were checking me out...
The romantic thing would be to say "I only had eyes for David", and while that is true, the fact is: I was as oblivious to their presence or interest in me as I was to David at that first party!
Hence: I HAVE NO GAYDAR! 
PS: Sadly, David passed away in 2017 as a result of a medical missed diagnosis. My heart remains, to this day, broken... 
!