There is nothing that will make an Englishman shit so quick as the sight of General Washington.
Source, in full
Retort attributed to Allen, during his captivity among the British, commenting after a picture of Washington was hung in a outhouse, in an anecdote told by Abraham Lincoln, as quoted in Lincoln, Vol. 1 (1996) by David Herbert Donald; the documentation on this is scanty, and it conceivably arose as a comical anecdote as early as Lincoln's time.
Notes from Wikiquote
It is most appropriately hung. There is nothing that will make an Englishman shit so quick as the sight of General Washington. | As quoted in Strange But True, America : Weird Tales from All 50 States (2004) by John Hafnor, p. 114 | It is most appropriately hung, nothing ever made the British shit like the sight of George Washington.