Then there's that whole pants vs. trousers potential embarrassment for North American visitors to the British Isles.

Pants = Trousers (North America)

Pants = Underpants (Britain)

Shorts = Short Trousers (Britain)

Shorts = Underpants or Short Trousers (North America)


And "bum", as an anatomical part, is considered a rude word over there.