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The repository for wildly inaccurate and/or grossly erroneous information frequently used by people attempting to provide an answer for something that they clearly do not know the answer to and/or for which they are obviously unqualified to answer but are too ignorant to admit it.

When expressing incredulity at a persons response to a question it is the more subtle and polite way to inform or identify an answer to a question that is clearly inaccurate by stating that the person must have gotten that answer from their rectalpedia britannica AKA "they pulled it out of their ass."
Ken:"Christine just asked me why I was not participating in the breast cancer awareness in the office and then she told me that breast cancer is the number one killer of men over the age of 35."

David: "What did you tell her?"

Ken: "I told her that was completely ludicrous."

David: "Yeah, no doubt another answer she pulled from her rectalpedia britannica."
by majordad June 30, 2010
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