improper vs sexual activity

improper is not a noun while sexual activity is a noun.

Word	Noun	Adjective	Verb	Adverb
improper	No	Yes	No	No
sexual activity	Yes	No	No	No

improper (noun)	sexual activity (noun)
	activities associated with sexual intercourse

improper (adjective)	sexual activity (adjective)
not suitable or right or appropriate
not appropriate for a purpose or occasion
not conforming to legality, moral law, or social convention