To bash someone is to verbally abuse them, usually with the intent of questioning their worth as a person (or a character, if fictional). The PPC does not approve of bashing anyone, real or otherwise.
Fanwriters sometimes bash a character, original or canon, and distort their personality or even kill them, because of the distaste the writer has for that character. The objective of character-bashing is often to get the bashed character out of the way so the writer's favored characters (and/or original character) can get with each other, or to provide angst, or make the story hurt/comfort.
If the character is put out of character, they are often turned into Designated Bastards of one stripe or another. They may be made out to be evil (if they are nominally good), to be stupid (if they are smart), to behave like a thirteen-year-old emo-teenager (when they usually are mature), and/or to be otherwise unlikeable, even to the point that characters who like them a lot in canon don't like them any more.
Killing the character gets them out of the picture much more easily, and can sometimes be disguised.
Bashing a character is a charge.
Author-bashing commonly takes the form of flames directed at the author in question, but can come in more insidious forms, as well, such as suggesting the author should be locked up in a mental institution for liking a certain pairing or type of fic, or that they must have been on drugs when they came up with their plot/OC/penname/etc. While not open insults, such remarks still have the effect of implying that there must be something wrong with the author as a person, which is not okay. Furthermore, they may be offensive to people who actually do have mental disabilities or other challenges—and put in the effort to overcome them.
Although we aren't perfect and do slip up sometimes, overall, the PPC does not approve of author-bashing. If Boarders catch other Boarders at it, they will most likely inform the perpetrator that author-bashing is Not Cool and request that they cut it out.