A nice illustration of a fallacy from The Simpsons:

After a single bear wandering into town has drawn an over-reaction from the residents of Springfield, Homer stands outside his house and muses, “Not a bear in sight. The Bear Patrol is working like a charm!”

Lisa sees through his reasoning: “That’s specious reasoning, dad.” Homer, misunderstanding the word “specious”, thanks her for the compliment.

Optimistically, she tries to explain the error in his argument: “By your logic, I could claim that this rock keeps tigers away.” Homer is confused: “Hmm; how does it work?” Lisa: “It doesn’t work; it’s just a stupid rock!” Homer: “Uh-huh.” Lisa: “… but I don’t see any tigers around, do you?”

Homer, after a moment’s thought: “Lisa, I want to buy your rock…”

Correlation does not imply causation. Just because two things occur together, does not mean that one caused the other. Homer argues that as the Bear Patrol vans are correlated with an absence of bears, the former must have caused the latter. Lisa, tongue in cheek, argues that as the presence of her rock is correlated with an absence of tigers, the former must have caused the latter.

At least Homer recognises that the two arguments are on a par, even if he fails to recognise that both are examples of the correlation not causation fallacy.