Contrary to what how we curse today, bodily functions were not the worst of the worst for medieval people when it came to swearing. Here is what Melissa Mohr, author of “Holy Sh*t: A Brief History of Swearing,” has to say:
“generally, people of medieval England did not share our modern concept of obscenity, in which words for taboo functions possess a power in excess of their literal meaning and must be fenced off from polite conversation…Medieval people were, to us, strikingly unconcerned with the Shit.”
People back then “did not have much of an issue with describing bodily functions in ways that we might find less appropriate. Going into a city you might find a street called ‘Shitwell Way’ or ‘Pissing Alley’. Open a school textbook for teaching children how to read and you might find the words arse, shit or fart. If you saw ants crawling around you would most likely call them ‘pisse-mires’. Even some names, like Rogerus Prikeproud or Thomas Turd, seem to have acceptable to medieval men and women.” http://www.medievalists.net/2013/11/08/by-gods-bones-medieval-swear-words/
Instead, really bad curse words involved taking the name of the Lord in vain. Mohr states: “certain vain oaths were believed to actually tear apart the ascended body of Christ, as he sat next to his Father in heaven. Phrases that incorporated body parts, like swearing “by God’s bones” or “by God’s nails,” were looked upon as a kind of opposite to the Catholic eucharist—the ceremony in which a priest is said to conjure Christ’s physical body in a wafer and his blood in wine.” http://newsfeed.time.com/2013/04/10/nine-things-you-probably-didnt-know-about-swear-words/
The above and the following reveal why ‘profanity,’ ‘swearing’ and ‘cursing’ are what we use to refer to this type of talk today, even though the words have lost their historical meaning to us. ‘Profanity’ is something that is ‘profane’–to corrupt the holy, in other words. ‘Swearing’ comes from ‘swearing an oath’–genuinely done at times, and ‘cursing’ is the same–people genuinely cursed other people. Here’s a book on ‘Benedictine maledictions’ where medieval monks between 990 and 1250 cursed their attackers. http://books.google.com/books/about/Benedictine_Maledictions.html?id=NRC_fLiVUJgC
And though the poor monk doesn’t actually use a profane word, he does curse the cat who peed on his manuscript (15th century):
Hic non defectus est, sed cattus minxit desuper nocte quadam. Confundatur pessimus cattus qui minxit super librum istum in nocte Daventrie, et consimiliter omnes alii propter illum. Et cavendum valde ne permittantur libri aperti per noctem ubi cattie venire possunt.
Which translates as:
Here is nothing missing, but a cat urinated on this during a certain night. Cursed be the pesty cat that urinated over this book during the night in Deventer and because of it many others [other cats] too. And beware well not to leave open books at night where cats can come.
By Shakespeare’s time, curses had swung the other way, partly due perhaps to the Protestant Reformation, leaving behind the focus on religious profanity. In medieval England, calling someone a ‘bastard’ or a ‘whore’ or insulting ther mother could always come into play, but Shakespeare was a master: http://www.museangel.net/insult.html