Why do people who have been to Japan (not born and raised in) act like they know everything about sushi?

You just provided the answer yourself. I hate it when Americans assume they know what real Mexican is, and all they know is Taco Bell and all the crappy joints in America which cater to American tastes.Or when they think that Spanish (From Spain) means Mexican or Puerto Rican, or Cuban. Sometimes I think they were standing behind the door during Geography class.

Sushi goes a looong way back in Japan, unfortunately the commercial, western version is what most of us know. Japanese would never add cream cheese to their sushi.

It sounds like you guys posters and postee, are a bunch of elitists. Why get upset if someone suggest a crappy place. It's not crappy to them, does that make them crappy themselves? They say "Little knowledge is dangerous." and what I'm seeing here applies to this specific question.
If it make them happy, why rain down on their parade. See what you guys are making me do, making me a walking cliche.
If someone like food at Taco Bell, so be it - why would someone say, don't eat that crap, go to Mexico for real Mexican food. American maki you can say is Japanese-American fusion sushi, America is about people of other ethnicities bringing their own cuisine and fusing it with American taste.
Doesn't mean that you had eaten something coming out to the sea within an hour make you better. I myself, like it that fresh, but I also appreciate what is available, packaged, and even frozen. If you only like certain authentic cuisine, then don't eat at all that is not that authentic, Sashimi grade that are served in Japan cost more than $300 per pound. Find a tuna of that quality, if you have the money to spend. There are only a handful of restaurant like that in the US, if you want to be so elitist, then just go to those places only, and not even step at any place lesser.
I think for people at Yahoo! Answer, shouldn't try to piss higher - because if you can, you won't be here in this site wasting your time and thoughts.
So those who love their Rock n Roll, Rainbow Roll, Caterpillar/Dragon Roll Maki, enjoy.

Isn't it obvious they're trying to show off!? It's true that just because someone's been to a country doesn't make them an expert at anything in that place. So if your friends are recommending crappy places then you're right, they're just trying to sound cool...

but aren't you doing the same thing, just in a much more subtle way? Saying, 'all my friends like to pretend they know a lot about sushi, but in fact they know nothing of tamago or the vinegar, salt, sugar mix that goes into a half decent sushi rice...'

Isn't your question like showing off while pretending to attack those who are show offs?

That's the reason why I've stopped answering questions on sushi. It seems the only "good" sushi that people recommend are Philly rolls, California rolls, or rolls that are made with cream cheese, etc. and when someone suggests sushi like uni, amaebi, aji, ikura, etc. they get a thumbs-down. And it's generally not people who's been to Japan who's the problem, it's those who's never been to Japan and have just "discovered" sushi recently because some non-Japanese sushi house around the corner.

And in regards to people can't tell the difference between good and bad sushi/sashimi, it's true. It wasn't until I visited Hokkaido that I learned how fresh uni's supposed to take like (fresh as in just caught from sea 10 mins ago), as compared to the "fresh" ones they sent here via air.

Simply because they can, really. If they've eaten sushi from the place it originated from, no doubt about it, they'd act like experts (even though they aren't)
But you seem to be passionate about this, and you seem to know alot more about sushi then them, right? So it's okay, just ignore them ^^

there are some people who lack the sensory receptors to tell the difference, but they are usually aware of that and don't try to recommend places to people with those receptors.
The type of people who recommend the crappy sushi bars are usually the social climbers who do so in order to appear cultured and refined and they think recommending what they think are authentic restaurants does so (in reality it makes them look like complete idiots)
My first taste of sushi was the good stuff, and eating that prepackaged crap that most sushi chains sell makes me gag!

because it's a cool thing to say..

Maybe they ate in crappy tourist-oriented restaurants in Japan, and then thought that's what it was supposed to taste like.

Because they are just plain silly...

The question is why people who isn't of south east Asian decent act like they know everything about ASIANs and there culture.........