Mean; contemptible; as, lousy knave.

Very bad; as, to feel lousy; to do a lousy job.

bad; contemptible

vile; despicable; "a dirty (or lousy) trick"; "a filthy traitor"

Infested with lice.

There are two definitions for this term: 1.) A varnish is termed "lousy" when it contains small particles of solid matter that were not removed by filtering. 2.) A brush is termed "lousy" if it contains particles of partially dried material that are transferred to the work.