abraham-man

from The Century Dictionary.

• noun Originally, a mendicant lunatic from Bethlehem Hospital, London.
• noun An impostor who wandered about the country seeking alms, under pretense of lunacy.

from the GNU version of the Collaborative International Dictionary of English.

• noun One of a set of vagabonds who formerly roamed through England, feigning lunacy for the sake of obtaining alms.
• noun to feign sickness.