I'd be careful here ... we have lot's of PR people who are members here and they pop in. Some of them might take you to task, about these types of comments.
Although some publicists may be "fake" in thier own right, I think that it's more the work they do that might create that feeling. Publicists have to be "on" all the time, espcially at events. They must cater to their clients, make everything smooth, make sure that everyone loves their client/product/company and smile while they are doing it ... whether or not things are going well. or whether or not they are happy about it. So, yeah ... that can certainly strain one's nerves and perhaps be hard to hide. So a person might seem to be fake ... when they are just trying to do their job under very difficult circumstances.
But that happens in most types of work ... you must pretend that you like your work your boss, your customers, your coworkers ... or you will be accused of having a bad attitude or not treating your customers well, or being a bod influence on the other employees. It's not just in PR. It's working in the real world .... where they expect you to show a positive attitude ... no matter what.