Top Definition
A condition that afflicts a growing number of newly-minted legal adults. It is characterized by the assumption that reaching the age of majority is carte blanche to do whatever one wants, regardless of any amount of protest from parents, authority figures, or even common sense. Most sufferers are observed stating something to the effect of "I'm 18, so I can do what I want!" upwards of twelve times daily, usually preceding a poor decision or the planning of one. Ironically, sufferers of 18 syndrome are often the most poorly-equipped members of their peer group when it comes to making decisions.

This condition is alarmingly prevalent among 18-year-olds who, despite being adults legally, lack nearly every quality that makes one an adult practically, e.g. responsibility, self-sufficiency, and maturity. In fact, the vast majority of sufferers depend on their parents for their livelihoods and still have close to a year of high school ahead of them. It afflicts both genders more or less equally, but a good rule of thumb is that it tends to produce bad decisions that cause physical harm in males and ones that cause emotional harm in females. Thankfully, beyond annoyance to others and the repercussions of the bad decisions it can frequently encourage, 18 syndrome is mostly harmless, and it seldom lasts beyond the age for which it is named.
"What's going on with our neighbor Martha? I know she's a smart girl, but yesterday I saw her tell her parents that they could fuck off because she was 18 and then drive off, cigarette in hand, with a pretty creepy-looking older guy. I'm worried for her."

"Don't sweat it. She just celebrated her birthday yesterday and now she has a really bad case of 18 syndrome."
by wearsmanyhats October 24, 2013

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