I found myself using a phrase recently which no-one in America seems to understand: "butters no parsnips". This is generally used at the end of short sentence describing a useless action.
For example: using the phrase "butters no parsnips" in the USA butters no parsnips.
My usual helper, Wikipedia, failed me, so I have to fly solo.
This phrase denotes that the action of the sentence does not help in any useful way. Buttering parsnips (ahead of roasting, perhaps), is clearly thought of as a positive outcome. This nifty little English phrase pours scorn on an attempt to do something by saying that the action will have no good outcome, not even buttering any parsnips (which, the phrase suggests, ought to be easy).
Of course, explaining this to Americans butters no parsnips, either.