mid-14c., lousi, "infested with lice," from louse + -y (2). Figurative use as a generic adjective of abuse dates from late 14c.; sense of "swarming with" (money, etc.) is American English slang from 1843. Related: Lousiness.
Bad; nasty; crummy: Crab was all she ever did. What a lousy sport/ Yuh lousy boob (1690+)
: I did pretty lousy on that test