Ms Li pulled strings to get Kevin good enough grades to pass and stay on the football team....until the very end of his senior year, when if he graduates, she'll, er, the *school* will lose its star athlete and winning record. Suddenly, Kevin's grades drop so much that he has to repeat his senior year. Anyone want to bet his grades rapidly come back up enough for him to regain his eligibility?
The Morgandoerfers are originally from Texas, as Beavis And Butthead was based there. It is very easy to imagine Daria being tormented there and developing her anti-social personality which she brought to Lawndale, even though everyone there pretty much lets her do her thing.
From The Daria Database: Quinn's Baby-sitting Spreadsheet makes note of Todd Green, age 8, who pestered Quinn to play games until she tricked him into Hide and Seek so she could watch a movie. Ha ha, typical Quinn right? Until you realize this neglected child, whom according to Quinn "walks funny and has a really round head" might actually be disabled.
Brittany's little brother is a Chronic Pet Killer, considering the fact that he is apparently the reason they don't name their pets anymore. In which case, what got him like that in the first place.