Ø I'm not aware of any profanity per se in the early Unix sources, but there certainly were some snarky error messages.   Like "eh?"   Or "Very Funny".  I contributed a few: "gummy structure".

Of which “You’re not expected to understand this” is probably the most famous.     This so incensed my mentor Mike Muuss that he figured out what the code REALLY did and wrote several paragrahs after that starting with “You are expected to understand this:”

The worst error system I ever encountered was a summer job I had in college.   The system I was using had a package called “reptile” that’s sole diagnostic was “Snake bite at xxxx” where xxxx was the address that the error was detected.   I had a crib sheet of what errors corresponded to what addresses, but that was rendered incorrect when the program was relinked and evertying moved.