Is American stand-up really like this?

In general, I'd agree that American stand-up seems to be more crass or louder, which I don't like, but there's certainly many American comedians who are not like that and are very good, or who are like that but do it in a funny way. George Carlin was amazing, Seinfeld is very smart, Chris Rock is great. (Not seen much Richard Pryor or Eddie Murphy stuff to be able to judge them). There's ones I don't like at all, like Dane Cook, Bill Hicks(sorry, I know he's revered almost, but all I've seen him really do is make political rants, which is all fine and well, but it's not especially funny), Andrew Dice Clay

My favourite comedians are all from the UK or at least have a strong association with the UK. Dylan Moran, Bill Bailey, Tim Minchin, Jimmy Carr, Eddie Izzard, Ross Noble, I'd not trade them for any US comedians. We've got our fair share of dross too, I find Peter Kay to be so awful, yet he's lauded as probably the most popular comedian in the UK.

And then.....AND THEN THE CAGE COMES DOWN!

Americans have been known for their stupid sense of humor. Honestly, it's unbearable. Most of them only love potty and sexual humor, which is why movies like Bridesmaids are so popular. Idiots, I tell you...

"When Gotham is ashes, you have my permission to die"-Bane

Bear in mind that the character who are trying to be stand-up comedians portrayed in this film are -- with the exception of George Simmons -- amateurs playing little dive bars where not only can they get away with vulgar material but the comedians are also not very polished and still have a way to go in their material and presentation. These are "open mic" amateurs who work day jobs. The material is kind of supposed to be a bit weak and inconsistent, not always clever and polished. We're being shown people who are wannabes, not professional standups, so obviously their material isn't going to be the best. The George Simmons character liked the main character's material enough to want to hire him, but we're still dealing with a guy who works in a deli and will probably never be as big as George or any real life standup of quality.

That's in the film. Back in the real world, among the standups who have made it to American mainstream, there are plenty of richly funny and talented standups. You don't get to see all of them in the UK because UK TV only imports but a tiny fraction of the entertainment happening in the US.

Lots of shows, comedians, etc do get to cross the pond, but not even half of what's actually there.

Personally, the type of comedy I enjoy is based on what makes me laugh, not on geography.

As "funny" is based on what is relatable, it should be no surprise that what you relate to, you find funny. A British comedian may make more jokes about upper class tea time or soccer hooligans and you may find it funnier than an American making jokes about trailer parks or racist cops killing unarmed blacks. It's not because the British comedian is funnier, it's because you relate to it so you enjoy it more. Do you really think less of Americans (or any other culture) for relating to it less and for relating to comedians who talk about the American experience (e.g Chris Rock) more?

Cultures are different all over the world, but people aren't. They laugh at what they relate to. Ironically - and contradicting your point entirely - for this reason what you would consider "low" humor (such as dick and fart jokes) are popular all over the world because men have dicks all over the world and all over the world people fart. Russell Brand is not popular all over the world because no-one outside of Britain cares about British politics, Oasis, or whatever he jokes about. He may be "funny" in Britain but, again, that's because people in Britain relate to his references.

The audience in the movie were fake, so they were laughing because the movie director told them to.

US standup is much better than what you see in this movie, and generally much better than what you get in the UK.

Check Bill Burr, Louis CK, Brian Regan, Jim Gaffigan, Doug Stanhope... all in my opinion better than everyone you mentioned.

"Hi, I've never really watched many Americans do stand-up with the exception of Chris Rock who's entire career revolves around imitating Richard Pryor and doing 'black jokes'. "

while rock admits, that he is heavily unfluenced by pryor and murphy, he did 3 absolutely outstanding standup routines, that are still legendary, when it comes to writing and delivery.

"I'm sorry but I've seen hundreds of comedians in the UK and every one of them blew the stand-up stuff out of the water in this film."

most of the people in this film were actors, not comedians. the only good routine in this film was done by aubrey plaza.

"Personally my favourites are Lee Evans, Russell Brand, Michael McIntyre, John Bishop, Peter Kay, Rhod Gilbert, Jack Dee, Jason Manford and Tommy Cooper (who's also a magician)."

sorry man, if you list russel brand and michael mcintyre here, then you are in no position to judge to begin with.
the other's are more or less debatable, but come back if stewart lee, dylan moran, ted chippington, bill bailey and jerry sawoditz are the first ones that come to your mind.