--Price of soft drinks
In Japan, I can be sure that a bottle of soda will cost 150 yen and a can 120 yen. Anything less (like a 100 yen vending machine or buying a bottle of soda for 88 yen at a grocery store) is a steal. However, most of the time, I can be assured that I will get ripped off no matter where I go. It's sort of nice to know--no matter what I do, which Lawson or 7/11 I go to, the price is uniformly expensive. Everyone is equally screwed.
In Hawaii/USA, the price varies depending on where you go. Some stores will sell it for a lot more (like an ABC store versus a Longs Drugs). It may still be cheaper than getting a drink in Japan, but it sucks to buy a 20 oz. soda for $2 only to find a vending machine down the street that sells it for $1.25. It's not the price. It's the principle.
--Being able to cuss/use slang without being understood
Don't lie--you do it too. When you can use words that would make a sailor blush because you know people around you don't understand... it's sort of natural to let loose. English in Japan is spoken somewhat (though less so in my area), but when you use slang and other colorful language, most people won't understand (with the exception of the F-word).
In other words, I have to watch my mouth in front here. I mean, think of the kids.
--Talking on your cell phone on public transportation
I know it's really not that big of a deal, and I used to do it too. But seriously? If you're going to talk on the phone on a bus, use an indoor voice. Your cell phone microphone picks up your voice fine, so there's no reason to raise your voice as if you're talking on a Nokia brick from the 90's.
In Japan, I've gotten scolded by an obachan only once for answering my phone on a bus. That was enough.
--Driving on the right side of the street
Not too much to say about this one, except that I've had my life flash before my eyes a few times because I now look the wrong way for oncoming traffic.
--Really obese people
Definitely rude of me to say, but I gotta say it--some of us Americans are monstrous. I definitely caught myself staring at someone the size of 4 fully-grown Japanese girls.
Even with my reverse culture shock, I must admit, it is nice being back in the states. It's comforting. I've forgotten how much I've missed the little things, like being able to read signs perfectly, seeing ethnic diversity, or even getting unlimited refills on soda.
Being that it's Hawaii definitely helps, too.
Waikiki Beach, Honolulu, Hawaii