Michael In five and a half years of living in the USA, I have gotten used to wearing a sort of sloppy California hacker look: short surfer shorts that come just below the knee with roomy side pockets (mostly from Billabong, DKNY, or Quicksilver), T-shirts that have been washed a thousand times (also surfer brands, but also Nike, Adidas, and some from the Costco supermarket in Maui, Hawaii), and sneakers that haven't been cleaned in years and are only half-laced (Mizuno Wave Rider) are what I usually wear -- my idea of a crossover between the Beach Boys and Public Enemy.
In San Francisco and the surrounding Bay Area, you rarely run into problems wearing this style: I only know of two establishments from which I was once kicked out for it: The cocktail lounge of the Bank of America building (no shorts or sneakers after 5:00 PM) and the bar room of the Fairmont Hotel (no T-shirts in the evening, must be a shirt or jacket). Since then, I've avoided these snobby hangouts during critical times and have been happily getting by with my choice of clothing.
In Japan, on the other hand, there is a stricter dress code: Most men wear suits with ties, and women wear business attire and high heels. This is because office jobs require this dress code, and people usually only go out with business colleagues after work without changing clothes.
Funnily enough, my experience was that even in upscale restaurants, you won't get kicked out despite having a shabby California look -— either you enjoy the exotic bonus as a Westerner, or such an affront would be far too embarrassing for the Japanese. I never tried it in shorts (it's not that warm in Japan in May), but even in the most elegant restaurant, my worn-out sneakers were neatly placed in front of the tatami mat without any eye-rolling.