improper vs sex activity

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

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

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

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