A terrible disease that typically effects only-children, but can occasionally strike people with siblings. It may also effect children whose parents divorce.
Symptoms include: playing mind games with members of the opposite sex, a cripling desire for instant gratification, the inability to compromise or share, and a total disregard for anyones thoughts or feelings but their own.
Example 1: Man, that girl is such a bitch- she wouldn't even spare a square! She has the worst case of only child syndrome I've ever seen!

Example 2: My boss has the worst case of only child syndrome ever! Every time I do something good he finds a way to slam me down just so he can feel better about himself.
by Andy Locoweed March 3, 2006
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Most commonly affects teenage guys. Only Child Syndrome is a terrifying disease to those who approach the infected. It most commonly infects only children, but in some rare cases people with siblings have been known to have the disease. Symptoms are selfishness, inability to comprehend other people’s feelings, and overall brat-like behaviour. If rejected in any way, for example, a breakup, those who are affected by Only Child Syndrome will most likely isolate themselves in an attempt for attention. Do not, under any condition, pander to these pathetic cries for attention. It’s all for a bit of drama.
Person 1: Mate, Alex told me that I would let him have my phone if I truly loved him!! How lame is that?

Person 2: Ignore him, it’s Only Child Syndrome.
by The better Anonymous January 15, 2018
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The self-centered attitude and actions that a large percentage of people with no siblings make their calling card.
Lars: "Why does he think everyone needs to worship the ground he walks on?"
Marv: "Dude it's just only child syndrome."
by Albiesaurus Rex October 26, 2008
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An incurable disease where the victim, after spending their childhood and adolescence in the endless days wallowing lonliness that comes along with being an only child, will prey on the opposite sex to fill the open role of an older or younger brother or sister in their life. this may be considered to be even sicker than a girl with daddy issues.

this often times only occours to children of white collar, yuppie, work-a-holic parents who tend to spend every waking moment neglecting their child for either work, buisness trips, or vacations with their husband/wife.

in almost every case of only child syndrome, the one kid was either a mistake or the opposite sex of what the parent was hoping for.
"jen is such a gold digger she only goes for rich older guys!"
"no, she just has only child syndrome, shes looking for someone to fill the role of an older brother!"
"ooh."

due to my only child syndrome, i was only friends with older girls in middle/high school, because i didnt have an older sister!
by giinny July 16, 2010
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Most commonly affects teenage guys. Only Child Syndrome is a terrifying disease to those who approach the infected. It most commonly infects only children, but in some rare cases people with siblings have been known to have the disease. Symptoms are selfishness, inability to comprehend other people’s feelings, and overall brat-like behaviour. If rejected in any way, for example, a breakup, those who are affected by Only Child Syndrome will most likely isolate themselves in an attempt for attention. Do not, under any condition, pander to these pathetic cries for attention. It’s all for a bit of drama.
Person 1: Mate, Alex told me that I would let him have my phone if I truly loved him!! How lame is that?

Person 2: Ignore him, it’s Only Child Syndrome.
by The better Anonymous January 15, 2018
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This is a sad disease that only affects only children with the rare case of divorce kids and siblings with a big age gap. This disease spreads in multiple different forms. Symptoms include being bratty, self centered, clingy, always searching for gratification, or being a total asshole. A poor child with this disease will only be effected by a few of these symptoms, never all of them.
Why is Jessica always so clingy? Yesterday I had to drag her while she clung onto my foot. She has major Only Child Syndrome.
by bri.l March 30, 2022
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Only children sometimes exhibit characteristics resembling women who have their periods. This can occasionally lead to flashes of intense anger when they don't get their way or someone insults them even the slightest bit. Also, when there is dissent in the friendship ranks which they are a part of, they lash out and try to make the other friends seem more culpable and especially more gay than they are. They have an overwhelming feeling that the world is against them and they tend to ruminate a lot as well. When you factor girls into the picture with an only child, it is never a pretty sight.
Garzon (on cell): Yo man, you wanna go play ball today?
Dre: Nah man, I got work today sorry
Garzon: God Damnit, no-one ever wants to fucking do anything in this town, i hate everyone. *click*

Later that night, Garzon ruminates for hours on how Dre is such a dick.

Garzon has exhibited traits that relate back to his "only child syndrome"
by darius jones March 18, 2009
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