Re: You know...
It's a long-running joke that the finance department and the IT department (or specifically the BOFH and PFY) have been at war almost since they started working there. This is just a continuation of that. Also, you have no guarantee that there was someone at PR who had a recent interaction with them and that they wanted to annoy.
More seriously though, every part of a business that does work usually has some usefulness to the rest of them. That doesn't mean that everyone will like them. This site is primarily read by people working in IT or development/engineering, so those departments in general get fewer insults (although the work of others in that area will also be described badly). Also from this readership, it is natural to hear more complaints about departments that frequently place obligations or restrictions on IT or engineering. PR is often not connected to those very often, while other departments are. For example, the following departments have these stereotypical ways of annoying the technical employee:
Finance: Refusing to pay for things that would assist the technology of the company, such as a more reliable backup solution or development resources.
Marketing: Primarily for engineering, agreeing to provide some technical product or service that does not yet exist and expecting the relevant department to create it without previously consulting them.
Security: Primarily for IT, placing restrictions on access which make it harder for staff to resolve technical issues.
And of course, I don't think you can talk very long to anyone outside of senior and middle management and not hear complaints about senior and middle management. When those complaints are made, general as they often are, they're not made purely out of malice. Neither are they always correct or well-measured.