pain in the neck vs pain in the ass

pain in the neck and pain in the ass both are nouns.

Word	Noun	Adjective	Verb	Adverb
pain in the neck	Yes	No	No	No
pain in the ass	Yes	No	No	No

As nouns, pain in the neck and pain in the ass are synonyms defined as:

pain in the neck and pain in the ass: something or someone that causes trouble; a source of unhappiness

Other synonyms of pain in the neck include annoyance, bother, botheration, infliction, nuisance, pain.

pain in the neck (noun)	pain in the ass (noun)
something or someone that causes trouble; a source of unhappiness	something or someone that causes trouble; a source of unhappiness