A friend who stays at your house for a month and then leaves without so much as a "thank you," is an example of an ingrate.
Origin of ingrateMiddle English ingrat ; from Old French ; from Classical Latin ingratus, unpleasant, ungrateful ; from in-, not + gratus, grateful: see grace
Origin of ingrateFrom Middle English ingrat, ungrateful, from Old French, from Latin ingratus : in-, not; see in–1 + gratus, pleasing, thankful; see gwer&schwa;-2 in Indo-European roots.
(comparative more ingrate, superlative most ingrate)
From Latin ingrātus (“disagreeable”), in- (“not”) + grātus (“pleasing”).