rude vs rudeness

rude is not a noun while rudeness is a noun.

Word	Noun	Adjective	Verb	Adverb
rude	No	Yes	No	No
rudeness	Yes	No	No	No

rude (noun)	rudeness (noun)
	a manner that is rude and insulting
	a wild or unrefined state

rude (adjective)	rudeness (adjective)
lacking civility or good manners
belonging to an early stage of technical development; characterized by simplicity and (often) crudeness
socially incorrect in behavior
(used especially of commodities) being unprocessed or manufactured using only simple or minimal processes
(of persons) lacking in refinement or grace