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 ingrātus in- not ; see in- 1. grātus pleasing, thankful ; see gwerə-2 in Indo-European roots.
(comparative more ingrate, superlative most ingrate)
From Latin ingrātus (“disagreeable”), in- (“not”) + grātus (“pleasing”).