One useful bit of Britspeak I have not heard for some time is the characterization of a social error as "bad form."

It was well illustrated in a scene in the Disney cartoon version of "Peter Pan." The villain, a cartoon version of Basil Rathbone as Captain Hook, becomes irritated by the singing of one of the pirates aloft. He pulls a piston from his belt, and to demonstrate his "cool" proficiency, without looking up, nonchalantly shoots the pirate dead. The mate, Smee, laughingly chides him "Bad form, Captain, you cut him off in the middle of his cadenza!"