Yep, it sure looks like Paul cussed.

More than that, I now regard all things as liabilities compared to the far greater value of knowing Christ Jesus my Lord, for whom I have suffered the loss of all things - indeed, I regard them as dung! - that I may gain ChristPhilippians 3:8

The word translated "dung" here is the Greek word skybalon. The word means rubbish, refuse, dung, and can refer to rotten or decaying things. The word is considered vulgar. The NET Bible has a note on the word:

The word here translated "dung" was often used in Greek as a vulgar term for fecal matter. As such it would most likely have had a certain shock value for the readers. This may well be Paul's meaning here, especially since the context is about what the flesh produces.NET Bible translator's note on the word "dung"

What English word is vulgar for fecal matter? Shit. Just like skybalon, "shit" is also used to describe rubbish.

This shouldn't be too surprising. Other verses use "offensive language," as well.

But Rabshakeh said unto them, Hath my master sent me to thy master, and to thee, to speak these words? hath he not sent me to the men which sit on the wall, that they may eat their own dung, and drink their own piss with you?2 Kings 18:27, KJV

We are all like one who is unclean, all our so-called righteous acts are like a menstrual rag in your sight. We all wither like a leaf; our sins carry us away like the wind.Isaiah 64:6

There are plenty of other examples of rough language and graphic analogies in the Bible.