"έχει το ακαταλόγιστο" means "he/she acts in an unreasonable way, but he/she is not to blame, because he/she is mentally ill.
ακαταλόγιστος, ακαταλόγιστη, ακαταλόγιστο is an adjective meaning "irresponsible, not trustworthy"
The phrase "έχει το ακαταλόγιστο" is also used as a legal term, when someone does not face a sentence for a crime due to a mental illness.
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Vasiliki Baskou, Instructor/Director, https://learn-greek-online.com.