Synonyms for Underbred (same or very similar meaning)
WordNet sense 1 ((of persons) lacking in refinement or grace):
ill-bred, rude, bounderish, lowbred, yokelishWordNet sense 2 ((used of persons and their behavior) not refined; uncouth):
unrefinedWordNet sense 3 (bred from a mixture of breeds or strains):
crossbredFrom the ODE community, based on WordNetadd/edit