dirty dog vs unpleasant person

dirty dog and unpleasant person both are nouns.

Word	Noun	Adjective	Verb	Adverb
dirty dog	Yes	No	No	No
unpleasant person	Yes	No	No	No

As nouns, unpleasant person is a hypernym of dirty dog; that is, unpleasant person is a word with a broader meaning than dirty dog:

Other hypernyms of dirty dog include disagreeable person.

dirty dog (noun)	unpleasant person (noun)
a person who is deemed to be despicable or contemptible	a person who is not pleasant or agreeable