Teenism

The inherent discrimination of teenagers by the rest of the population. Commonly assumed to be mentally deficient, whiney, ungrateful, lazy, and other negative traits. Often incited by the age old perception that has been passed down through generations. Can be immensely frustrating for a teenager, as they are often spoken to condescendingly or treated as an inevitable criminal.
Note that this is not limited to adults discriminating against said teenagers. Teenagers can discriminate among their own age group, or adolescents slightly younger/older.