Ikenuma was born from an abbreviation + mistranslation. People with intellectual disabilities were originally referred to as "mentally disabled" on the internet, but since "chisho" doesn't come out even when converted, it has the same meaning. Ikenuma is a word used mainly in the 2channel area to mean a person with an intellectual disability (person/child), and is said to have originated there. Intellectual disability (person) (chikisho gargar (sha)) → knowledge. Original meaning (main image is this). A slang word that uses the homophones for ``mental disability,'' which is an abbreviation for ``intellectually disabled person.'' Derogatory words, discriminatory words. (Related to 2) The person's speech and behavior are so incoherent that an intellectual disability is suspected.
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Summary: It is one of the 2channel terms. The etymology is mentally retarded person → intellectual disability → chisho → ikenuma (kanji on reading). This term refers to people who make incompetent comments, not necessarily because they actually have an intellectual disability.
