1 definition by Brian Adelman

Top Definition
an intellectual state in which one is of well below average intelligence.

100% of the time, the mentally fat person is completely unaware of their intellectual condition.

Note: Physically attractive people can most certainly (and often times are) mentally fat.
Man, she was so hot but seriously, that girl is so goddamn mentally fat I could not stand another second in her presence.
by Brian Adelman May 01, 2010

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