I've had varied experiences here and there, not everyone at one park is a cretin and not all cretins go to one park. You'll find idiots no mater where you go, even at some of the nicest parks. However, places where I've noticed bad behavior seems to be more common than usual are in no particular order:
*Six Flags Magic Mountain
*Six Flags America
*Dollywood (sometimes, mostly when it's more crowded)
*Holiday World (again, see above)
*Kennywood
*Mt. Olympus
*Busch Gardens Tampa's clientele wasn't necessarily badly behaved, but I did hear a lot of stupid comments tossed around the midway such as "oh no sweetie, we don't ride those you can break your neck on those things," and "they're the fastest, most agile animals on the planet, there's no way they can't jump out of that fence."
This of course excludes parks on school group days. Because if there are school groups on a day when you go, no matter what the park is, it will be full of 13 year-old clarinet players with their fidget spinners climbing on queue railings.