short bus window licker
Somebody profoundly lacking in personal dignity and social grace. While not actually mentally disabled, such persons are often so enabled by family members or sympathetic friends that they become hopelessly unaware of the ridicule, revulsion, or downright murderous rage that they evoke from everybody else.
I don't care if he's our ride home. If that short bus window licker doesn't stop yelling at the movie screen I'm going to break a bottle over his fucking head.