sex activity vs bodily function

sex activity and bodily function both are nouns.

Word	Noun	Adjective	Verb	Adverb
sex activity	Yes	No	No	No
bodily function	Yes	No	No	No

As nouns, bodily function is a hypernym of sex activity; that is, bodily function is a word with a broader meaning than sex activity:

Other hypernyms of sex activity include activity, bodily process, body process.

sex activity (noun)	bodily function (noun)
activities associated with sexual intercourse	an organic process that takes place in the body