When I moved to the States 15 years ago, I was grossed out by PB&J as well. I grew up on peanutbutter and sambal - an Indonesian hot sauce. I will still eat peanutbutter and hot sauce sandwiches once in a while and sometimes I can get hold of sambal. Delicious.
Over the last 15 years I have lived in the Mid West, Israel, East Coast and near Manchester England. A short sampling of customs brought up by this thread:
Hitchhiking in Israel. Nonchalantly point to the place where you want the car to stop with your index finger. The raised thumb means “sit on this” in several middle eastern cultures. Not a great way to get a ride.
If you want someone to wait a second, bring your hand in front of your face, palm up, bring fingers together and say “tehh, tehh”.
Raised middle finger is inverted: you stretch out yor hand with palm to the ground and point your middle finger down while holding rest of the hand outstretched, or bring your fore arm up while hitting your biceps with opposing hand. Both mean ‘f*ck you’.
Kissing as a form of greeting in Holland. I think that we were the first generation where males started kissing each other as frequently as females. I am from the South, so it is indeed three times. Just over the border in Flanders I have seen people go at it 4 times. Now that is strange.
Tips in restaurants are at your discretion. A euro can be a handsome tip.
What struck me as strange in the US? Supermarkets, there is just too much choice: why do you need so many different kinds of toilet paper for example? When I left the Netherlands 15 years ago, there were essentially two kinds: the rough, cheap stuff that would make you bleed after prolonged use and the expensive soft stuff that never cleaned you completely. Why would anyone ever need anything else?
I was also baffled by people asking me “How are you?” and then continuing to walk, without stopping to listen to my answer.
Really friendly people who tell you everything about themselves who do not remember you the next time you meet.
England: I told someone that they did a good job on a presentation. They came to me afterwards and politely asked why I did not like their work. I told them I did. I should have said: “Not bad”, that is way better than: “Good job!”.
I am sure more will come to mind.