Someone who suffers from a mental disorder and delusions of grandeur. Someone who has lost touch with reality. Could be just depressed but rans the gammit from depression to schizophrenia.
Man, that Mike Rehmeyer is mentally ill. He's 34, lives at home, has no college education and nothing going for him yet he thinks he's Prince Charles.
by arfed February 12, 2008
mentally ill is someone they called a good person or a super hero that they can't fake a crime on or put in prison so they try to make him look crazy and put him on psych meds to make him crazy for real to look him up in a mental hospital forever
you are mentally ill, go talk to a therapist. you got therapist money?
by Megasus Thrist Jesus Christ April 27, 2022
Driving 5 hours just to go to waffle house while high on edibles.
you must have Mental Illness if you would drive 5 hours just to get waffle house
by Nai_OG January 13, 2022
An illness that inflicts the person's mental state. Mental illnesses range widely from mild anxiety to severe schizophrenia. Depending on the severity of an illness, it can impact a person's life more than just mentally. For example, a person with borderline personality disorder might have a hard time holding down a job because of their mood instability. Other things that can be hard while mentally ill are keeping good hygiene, keeping healthy relationships, and keeping a good sleep schedule
John breaks up with Becky's best friend.
Becky: That was so sick of you! What, do you have a mental illness?

John: Mentally Ill is not an adjective. I have though, been struggling with depression. My mental ill ness doesn’t make me any less of a person.
by PurplePanda4 February 28, 2021
A defect in the minds function. But does not nessercerily affect your intelegence. Saying a mental illness makes you crazy/stupid/funny is like saying an eating disorder makes you fat.
Bill Gates, who is a multi-billionare, invented the personal computer, is very creative and in the top ten smartest men alive suffers from aspergers syndrome, which is infact a mental illness.
by GavinBobJones November 4, 2006
A metaphoric and ad-hoc term for human suffering used paradoxically alongside "psychiatric disorder" and is often force applied just prior to what UN definition defines as psychiatric torture. There's no way of proving a "mental illness" but that won't stop Janet on facebook claiming you're "mentally ill" and "need treatment" AKA chemical or electrical alteration, just because you offended her primitive sense of reality and humour. Logic has never stopped a psychiatrist either.
"Well I disagree with your premise. I also possibly can not negate it! I may be gas-lighting you or engaging purely for personal gain or profit. Yes, I am probably attempting to discredit you rather than the premise or the experience by using pseudo-professional psychiatric character assassinations, and there may be no way to prove it but you sir have a mental illness"!

"I don't like your politics, you are mentally ill"

"If you don't take your joy pill you'll express your true feelings then get mental illness. Off to the psikhushkas!"

"Difficult childhood, because mental illness. Wait, no, that was a false biological causation".

"Your child won't act like an adult? Give him this kiddy speed for his mental illness, you're welcome."
by EndPsych May 16, 2017