sex activity vs nasty

sex activity is a noun but nasty is not a noun.

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

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

sex activity (adjective)	nasty (adjective)
	offensive or even (of persons) malicious
	exasperatingly difficult to handle or circumvent
	disgustingly dirty; filled or smeared with offensive matter
	characterized by obscenity