I love the differences between american usage and british usage that make transatlantic chats so interesting. Not so much the words which are just a matter of preference, like torch / flashlight , bumper /fender, trunk / boot but more like the word hood which in relation to a car for an american would mean the same thing as a brit would refer to as the bonnet (hood would normally be understood to be the roof to a brit). Those don't usually cause much confusion because we are all used to them but there are words such as "jumper" which a brit would use to refer to the item which an american would call a sweater, if an american used jumper he would probably be referring to an item a brit would call a gymslip.
In the UK if a "motion is tabled" it is put up for discussion whereas americans use the same phrase to mean that it is taken down from discussion. Similarly a "Moot Point" to a brit is one which is worthy of and should be discussed but to an american a "Moot Point" is one which does not warrant further discussion.
I'm sure we all know of hundreds more words which have different meanings in american and british english, but we probably aren't all aware of the same ones. I was chatting with an american buddy recently about the word "okay" which is in common usage on both sides of the atlantic but with slightly different meanings. We can both use it as an affirmative but if he uses it to describe how his day went he means it was a good day, whereas if I used it to describe my day, it would mean that although nothing went particularly wrong it wasn't a good day.
So will this thread go down a bomb (british english for do really well) or will it bomb (american english for do really badly)? Post all the words that you can think of which might be confusing to speakers of brit/eng or am/eng or even dialect words which are confusing to others who speak the same version of english I think Ade mentioned in one of his posts how confusing the word "while" can be, depending on your locality.