Moral Event Horizon: Hobgoblin's comes after He has Mary Jane killed and then repeatedly mocks Spider-Man about it. Alternatively, his blowing up the Daily Bugle for no other reason then because J. Jonah Jameson refused to print his story about Peter Parker being Spider-Man and taking sadistic pleasure in that too could also be his MEH crossing.
Scorpion's comes when he killed Mary Jane the deed on Hobgoblin's orders. Its implied that Carnage's came a long time ago.
Nightmare Fuel: Spider-Man's beating of Scorpion after Gargan kills his wife is pretty vicious, and the story makes it clear just how single-minded Spider-Man is in his goal of killing Scorpion. He even plans on ripping his tail out, fully aware that that will also take out Scorpion's spine Thankfully, Black Cat arrives and manages to talk him back to sanity, just as the real Big Bad Hobgoblin arrives to attack him.
One-Scene Wonder: Many. The Enforcers, Flash Thompson, Lizard (but not Curt Connors), Electro, Rhino, The Wrecking Crew, Human Torch, The Thing, and at the very end Gwen Stacy are the most prominent examples.
The Woobie: Spider-Man big time. Of course, he usually gets that role in mainstream continuity too...