Maybe it's because the comedy was a little on the weird side, but the british already knew the character. There's also another element to all this. If you take something like the horrendous bloodthirsty ravings he managed to stir up at the rodeo, the point isn't so much whether Borat is funny (which varies), or that he temporarily upset the Kazakhs. The funny thing is that he was showing, in a lot of the scenes, something of the country he was visiting. It wasn't the Kazakhs that were being taken for a ride, but the people inthe film. Is it possible that this may make it less popular in the States than it is in the UK, and perhaps this is a factor in who finds it funny. There is an argument that Borat is so obvioulsly ridiculous, that he's not the bit of the film that's ultimately so gross.
Though this is obviously a reflection of some of the ridiculous things he found in the states, you can all take comfort that, as Ali G, he did EXACTLY the same in the UK. Seeing politicians, religious leaders etc trying to grapple with this monster of a creation, who they believed to be real, was just so very revealing. But, as mentioned - sometimes it works, and sometimes it falls flat. I just hope he doesn't come to visit the place where I live!! The attitudes of some people would REALLY be cringeworthy to watch!
I'll admit that I do not know very much about this actor. Though, I saw a few minutes of the Ali G show on HBO one time and promptly turned it off. I have two thoughts about it. I love humour. I don't think something has to be vulgar or offensive in order to be funny. Second, I think there is a fine line about joking about normes, mores and values that can be funny and can be flat out offensive, hurtful, and only funny to a select crowd; the select crowd being the people who are not the target of the joke.
There is plenty of humour out their that can make fun of things without offensive jokes and forces us all to look at our own normes, mores, and values and have a laught at them only at the expense of ourselves. Monty Python was at times able to walk this line. Woody Allen might be the master of it. Mel Brookes did it with Young Frankenstein. Sorry can't think of anybody recent at the moment though Scoop was good. Everything I have read about this film and Ali G makes me think he is part of the hurtful and offensive crowd which is only funny to people who are not the target of the joke.
"Perserverance and spirit have done wonders in all ages."
~General George Washington