Post Grade 11 Syndrome
Post Grade 11 Syndrome (PGES) is a phenomenon that occurs during the high school years, often as a result of excessive partying, drug use, or other activities that have a negative effect on brain function and development. It is usually not noticed right away by the sufferer, but becomes more apparent in hindsight once a substantial amount of brain cells have been killed off. Symptoms of this syndrome include but are not limited to: walking into rooms and forgetting why your there, forgetting facts you found easy to remember in middle or grade school, and hooking up with people and having a hard time remembering their names. In short, Post Grade 11 syndrome is essentially a slow process of generally going down hill that begins during high school, and ends whenever you actually grow up or die.
guy 1: 'Man, I totally just walked into the kitchen, opened the fridge, stared at it for like ten minutes, forget why I was there, and then left the kitchen with a water. I used to have my shit so together my brain just feels like its melting.'

guy 2: 'You're right, you definitely peaked in grade 10, you totally have Post Grade 11 Syndrome.'