The Volokh Conspiracy
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"Mentally incapacitated" means that a person is temporarily incapable of apprising or controlling the person's own conduct due to the influence of a narcotic, anesthetic, or intoxicating substance.
If you don't get the Iceberg, Goldberg, see here. I should note that one of the several dictionaries I consulted, dictionary.com, says that "appraise" is an obsolete definition of "apprise," but the Oxford English Dictionary, usually a more reliable source for archaic definitions, doesn't include it; and the statutory provision dates from 1999.
UPDATE: Commenter h c m writes:
This is almost but not quite an ad homonym attack on the statute.