dirty word vs do it

dirty word is a noun but do it is not a noun.

Word	Noun	Adjective	Verb	Adverb
dirty word	Yes	No	No	No
do it	No	No	Yes	No

dirty word (noun)	do it (noun)
an offensive or indecent word or phrase
a word that is considered to be unmentionable

dirty word (verb)	do it (verb)
	have sexual intercourse with