Then the OP should stay home until they learn how to behave in public. That it needs explaining AT ALL is a trip. 

Differences in the sound mixing & the purpose of the performance.
A concert typically has the volume cranked up, even on the soft songs, so the rest of the audience can still hear the performer even if people sing along. And the show is about “hey, here’s a bunch of songs you probably like by a performer you like, have…

So, this is a video of what she was doing. She wasn’t like, quietly singing. She was disruptive AF. But also in general, a concert and a theatre show are two different things, with different expected etiquette.

“How are you not gonna belt out the chorus of “I Will Always Love You” when the spirit of Whitney takes you, huh?”

Which is hilarious because the whole reason the Beatles stopped performing live is because they couldn't hear each other or themselves over all the screaming. 

Yeah, I’m not sure when everyone decided that was the world’s greatest song.  Back in the day it was just sappy and ridiculously overplayed.  Dolly’s version is at least more understated.  

Because no one paid to hear you sing. It’s not always about you dear.

It’s one thing to sing along at a concert. At a play/musical? Stfu. 

First of all, Jersey Boys is SO FUN.  Second of all, that happened to me when I saw Wicked. Someone behind me was singing along to every song.  Like, stay home and listen to the soundtrack if you jut want to hear your own voice.

I saw Jesus Christ Superstar a couple of months ago, which was the first non-community live theater I had seen in a LONG time. When “I Don’t Know How to Love Him” started, the woman next to me started singing along, but really, really quietly.

This is actually part of a long set of complaints in the British theatre world with the audience, as they get to the show very drunk and make a mess, shout at the stage, start brawls, that stuff.

I remember it being no.1 in the charts for at least 4 years , and you couldnt avoid it , so

Concert: sing along. It’s encouraged, unless it’s intended to be a specially quiet, intimate song (and even you can, as long as it’s not making it hard for others to hear the singer).

If you want to WATCH Rocky Horror watch it at home (it’s not very good). The whole point of going to a show is the audience participation and shad0w-cast. 

At Linda McCartney’s memorial service the surviving Beatles came together to perform “Let it Be” in her honor, and the story goes that the moment they started playing what was meant to be a very personal tribute to Linda, everyone in attendance joined in, unbidden, like it was a singalong. As a result, the Beatles…

I’ll go to a movie during the slow time of day when there are only 10 or so people in the theater, but I won’t go back to a live performance until they get a better handle on Covid.

I think that’s the joke. 

DEATH HAS SPOKEN!

Concerts, shows, even movies these days are a “no thanks” for me. People post-Pandemic are getting awful. If this is the ‘new normal’, no thanks. I’m there for the show, not the side-show.

“Two women were forcibly pulled out of the theater by security”