43

A 43 means a mentally disturbed person to the Akron Police Department in Ohio.
This term was popularized due to the infamous lolcow Cyrax who was referred to as a 43 by the Akron PD.

Cop 1: did you get called up to Chance Wilkins' house again too?
Cop 2: yeah, he's totally a 43! Have you seen his YouTube channel?
Cop 1: Yeah man, he is absolutely vile!
Cyrax: I AINT NO FUKIN 43