A problem with having a reputation for being funny--or so I've heard from people with such reputations--is that people then expect you to be able to be funny on command. A friend of mine, "J.", has even had people stop by his office with visitors and introduce him with something like, "This is J., he's funny." How on earth does one respond to that? Is he expected to break out into a stand-up routine right then and there in his office? Maybe even a full-fledged hallway-comedian show with props: a unicycle, one of those fake cans of peanut brittle with the spring-loaded snakes inside, some balls to juggle, a dancing marmot, all accompanied by a laugh-track set to run from his computer.
My experience talking to people with weblogs is that most people who write amusing posts hate to have their weblogs characterized as being in the genre of "humorous" or "funny" weblogs, partly for the light'n'airiness it may imply about their bloggerly lives, but more because they don't want the pressure. As a broad-generality-with-certain-exceptions, if someone proudly advertises their as being "humorous"/"funny", it's probably not actually very humorous/funny.
In any case, poor Dorotha. Not only does she suffer the expectation of some that she will be witty and amusing on command, but she also has to deal with the expectation that she can be mean on command as well. It would seem to me to be difficult to get off both those hooks simultaneously. That is, everyone recognizes that a funny person might sometimes not be in a mood to be funny, but you would think that if a mean and funny person was not in a mood to be funny, the least she could do would be to be mean about it. (For the record: Dorotha greatly exaggerates her mean-ness. She is, however, funny. And much better to be funny-but-not-as-mean-as-she-thinks than to be mean-but-not-as-funny-as-she-thinks.)