WordNet sense 1 (not conforming to legality, moral law, or social convention):

unconventional, unlawful

WordNet sense 2 (contrary to rule or accepted order or general practice):

irregular

WordNet sense 3 (not in accord with established usage or procedure):

wrong

WordNet sense 4 (not in keeping with accepted standards of what is right or proper in polite society):

indecent, indecorous, unbecoming, unseemly

WordNet sense 5 (not appropriate for a purpose or occasion):

unsuitable

WordNet sense 6 (not suitable for a particular occasion etc):

inappropriate