When one person feels they have a rivalry with another far superior person. The superior person usually doesn't know about it or feel that the little brother is any kind of a threat. The little brother usually puts forth maximum effort in meaningless situations in order to get the feeling of a win over his rival.
The Baltimore Raven's fans have little brother syndrome. They think they are the Redskin's rivals.
by persephone81 August 13, 2009
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When a younger brother is bigger or around the same size as the older brother. sometimes the younger brother will have a very low,sometimes lower voice then the older brother which is rather comical.
My Brother's friends were horrified when I was introduced as his "little brother"

"More like my Big Little Brother" He corrected.
by Kelly Day October 22, 2007
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Knows exactly which buttons to push. He says he didn’t know any better but I know the truth.
God, my annoying little brother just shoved my last 6 tampons up his nose
by Brewers yeast December 18, 2017
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usually the middle child in a family who is trying to show up his older sibling.
"damn Tyrone, Drew got that {little brother's disease}! Why he always gotta be up in the mix?
by infidellicswaggernaut April 24, 2016
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An ingrained fear reaction that younger siblings show towards an elder. If properly nurtured can result in reactions such as flinching when the older sibling walks past even though the younger is taller, bigger and stronger and 18+. This can also result in a defeatist attitude and outcome when in confrontations with the older sibling.
Luke was a victim of little brother syndrome. Even though he was bigger, stronger, faster and a black belt in karate he could never defeat his older brother in a tickle fight. Luke is 20 years old.
by Rincow April 15, 2011
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When an older sibling brings a best friend into their home and the littler sibling thinks said person is their new friend and tries to impress them/flirt/or just won't leave you too alone for any reason
Your little brother has "Little Brother Syndrome" when he keeps trying to show your best friend his vast collection of Hot Wheels, even though said friend doesn't care and you both want him to go away.
by Dr. Upin Disbich July 5, 2015
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When a person(doesn't always have to be a sibling) idolizes something you have done and decides to follow in your footsteps, ultimately copying exactly what you have done; complete and juvenile lack of originality.
My friend has little brother syndrome. I began to pursue my dream of writing comic books, and not to my surprise, i find the hack doing exactly the same.
by xX Unwise Xx January 13, 2010
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