Fake names
It's been generally agreed that it's okay to use the name of a celebrity for an obvious joke.
It would not be okay to use the name of a celebrity if there was a serious attempt to make people think it was really the celebrity. This is more of an issue for middle-level celebrities who might actually post here.
It is also not okay to use the name of a random celebrity to disguise the originator of a flame or some controversial statement.
There's some gray areas. It's kind of a judgment call.