When I saw Boeing-Boeing, there were many people who laughed loudly throughout the show, but it didn't bother me.
I don't think that I am a particularly loud laugher. But, I have been in a situation where there was me and one other person laughing at the same moment in the show. This was one of the times I saw Spamalot, and during You Won't succeed on Broadway, there was one guy and I who were cracking up during the entire song. By the by, that song never fails to crack me up no matter how many times I have listened to it. I did find it interesting that the other people around us in the balcony had looks of shock as to say that they couldn't believe that they were singing a song with that particular subject matter and that me and this other guy were wrong for laughing at it.
I have a very loud laugh and I know it so I tend to cover my mouth/try to keep it quiet when I'm at a show.
When I saw The Producers, a woman in the audience laughed very loudly at EVERY SINGLE THING that Nathan Lane said. Even if it wasn't a punch line. Even if it was just a regular piece of dialogue that wasn't supposed to be funny. It was kind of ridiculous, and the audience started laughing back within the first few minutes of dialogue. Fortunately, Lane put an end to it pretty quickly by looking out over the audience with a puzzled look after her loud laughter after an ordinary line and ad-libbing something like, "Because what I said was so funny" or something like that -- it was hilarious and did not come off as mean-spirited (I can't remember exactly what he said, but it was more clever than what I just wrote), and she calmed down.
I find the people who seem to be insincerely laughing too loudly to be extremely annoying. If someone is finding the show funnier than I do, that's one thing, but if someone is forcing it, it is very distracting.
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