Unintentionally Unsympathetic: While most of her problems with Ferguson were pretty valid, there were a couple instances where she seemed like a bully. For example, in one episode, Ferguson seeks her for advice on how to properly date a girl he has a crush on. She deliberately gives him the most outlandish suggestions she can think of to sabotage his relationship with her. Granted, this backfires, but it's still a pretty mean and bullish thing to do.
There's also a dream sequence in one of the final episodes in which Clarissa kills Ferguson (really!), and he comes back as an angel and/or devil. They only hint at it ("the man upstairs" and "the great beyond"), but in the dream, he is dead, their parents fall apart (her father becomes a hippie who constantly mourns for his dead son and her mother takes up smoking) and Clarissa seems like she is barely concerned.