Quote from momimomi
School Days is based on a game
If you play games, I don't know if you already played it and/or are interested, but to me the most downhill stuff I ever saw is Chaos Head, route B. I don't think something can go as bad as that.
Unluckily, I really can't think of a manga with all the features you want. Maybe Narutaru (same mangaka as Bokurano), but I still have to read it all.
What I like in Trivial Pursuit style. Pick your category: