I like this topic and I can think of a hundred things I've had to explain to my wonderful, and caring hubby, so here's a few just off the top
1) why we have gallons of milk, gallons of juice, gallons of water - heck gallons of anything for that matter
2) why everying over here is soooooooooooo huuuuuuuuge, (cars, houses)
3) yes you do have to stop at the "stop" sign even if no one is there and doubly especially if a cop is nearby
4) you can't just park in handicap spot because you think no one is there now
5) CREDIT CARDS - as a newcomer to the states its not a good idea to call every bank or credit company to try to get a credit card. it counts against you when you are established long enough and that's called 'inquires' to your credit. a great big NO NO
6) minimum pay due does not mean you pay only the minimum
7) just because you speak good english (which he does since he learned the British way

) doesn' t mean that we understand what you say all the time
8) yes its ok to go to IHOP at 3 in the afternoon and eat pancakes, you can even eat pancakes, eggs, toast at 3 in the afternoon if your at home
9) if you don't put the food in the refrigerator overnite, it'll go bad
10) you have to wait in line at restaurants, banks, grocery stores, there is no skipping