dirty vs muddy up

dirty is an adjective but muddy up is not an adjective.

Word	Noun	Adjective	Verb	Adverb
dirty	No	Yes	Yes	No
muddy up	No	No	Yes	No

As verbs, muddy up is a hyponym of dirty; that is, muddy up is a word with a more specific, narrower meaning than dirty:

Other hyponyms of dirty include foul, contaminate, foul, pollute, smear, slime, muddy, splash, mire, muck, muck up, mud, crock, blemish, spot.

dirty (adjective)	muddy up (adjective)
soiled or likely to soil with dirt or grime
(of behavior or especially language) characterized by obscenity or indecency
spreading pollution or contamination; especially radioactive contamination
unethical or dishonest
expressing or revealing hostility or dislike
obtained illegally or by improper means
(of a manuscript) defaced with changes
(of color) discolored by impurities; not bright and clear
vile; despicable
contaminated with infecting organisms
unpleasantly stormy
violating accepted standards or rules

dirty (verb)	muddy up (verb)
make soiled, filthy, or dirty	dirty with mud