I was always taught that Americans don't put butter on their sandwiches. Is that true, or just a myth?
As tux indicates, it varies. It also depends on the sandwich. From my own observations:
For plain toast, people would use butter.
For grilled cheese sandwiches, butter goes on before you grill it. (I have seen Jelly put on top after cooking, but that's uncommon)
For peanut butter sandwiches, I've seen with/without butter.
For peanut butter and jelly sandwiches, no butter generally.
For deli meat (ex ham) and cheese, mayonaise is very common, butter almost never.
For a hamburger, mayo is common, butter only if the bun is grilled (for lightly toasting)
For a sub (subway, quiznos, Jimmy Johns) no butter in sight.