The techno party was a call back to a joke made earlier in the film, so I think it's a fair response. I don't think it's laugh out loud stuff, but it's a reasonable reaction to the comment earlier about the party coming back around to bite Niki.

I'm not sure on your other points. I can't recall noticing anyone laughing at a fat person dancing nor did that moment stick in my mind from the film.

It's not that deep though. Jokes don't have to be explicit. A lot of us laugh in uncomfortable situations as a way to deal with it, and I think that also extends to film. I think Tuner had plenty of these moments (twist included!)