Whether you're on a dancefloor, at a bar, or in a concert crowd, no one around you cares that you know all the words to a song nearly as much as you do, even if you just casually sing a part or two juust enough to convey your knowledge of the song without going overboard (in fact, you know it SO well, you can't control yourself, you just naturally have to sing a part!!!)
Either way, no one around you is impressed. Even when you overly-mouth the words at a loud concert so the people around you know you're singing along and thus a TRUE fan. The only person who cares the least bit about your overt 'True Fan'-ness is yourself.
When you're watching tv and some semi-obscure character actor shows up that you recognize, it's nearly impossible not to immediately make this fact known to anyone else in the room around you, either by casually being like "oh cool, it's Bubbles from The Wire", or by going the extra mile and saying the actor's name, or by the only-slightly-less-subtle approach of yelling "I RECOGNIZE THAT ACTOR EVERYONE IN THIS ROOM! I WIN THE TV RECOGNIZEY PERSON GAME THAT JUST STARTED AND ENDED RIGHT NOW."
I'm not judging, by the way, I do this more than anyone. But then when someone else does it, I never care, because if I did care, I would've recognized the person. "Oh, it's a character I don't know from a show I never watched? Cool."
"Whoa, did you hear about that library that collapsed in Spain? The video is crazy!"
"Yeah. I studied abroad in Madrid one summer. Not near there. But I knew about the library. But anyway yeah, crazy video."
"Also I ate authentic paella there. That's only semi-related."
"This actually kinda reminds me of the book I'm reading right now, it's called--"
[You instantly tune out unless it's a book you already read, which 95% of the time it isn't, so you just politely nod your head until you get to tell them about the book YOU'RE reading and they can do the same]
Wait, so you went to Vegas last weekend, sat down at a Blackjack table, and won $40? That's the story? A minor good thing happened to you? Why would I want to know about that? Actually, why would I want to know about any good things that happened to you? What's next, are you gonna tell me some stories about a Tinder date that went very well?
"Holy shit, did you see Game of Thrones last night?"
"Ohhh mann!!! No I haven't but I saw the dude who plays Baelish at a Coffee Bean once."
"Really? What was that like, did you say anything to him??"
"No, he was leaving. I think he got coffee."
"Oh. Cool. One time I saw Jessica Alba on the street."
"Wow, I had the most ridiculous dream last night, you have to hear this."
"Oh man, really? Was I in it?"
"No, but t--" [INSTANT TUNE-OUT]
The only people who ever actually want to hear about something good happening to you are your parents, your significant other, and maybe your closest friend (and even then, one of them might be secretly jealous of you, or hoping the story keeps going and something funny/shitty happens to you in it, thus making it a better story.) The rest of us? We don't need to deal with your stupid "casual friend who had something good happen to them" crap.
Unless, of course, I just talked about something good that happened to me, in which case, of course I'm happy for you! Why wouldn't I be?? I'm a great and selfless friend.