I haven't had a nightmare since I was about 7. The scariest dream I ever had was...
At the beginning, there was an elegently dressed adolescent girl making an ice sculpture. Then she suddenly got up and left the building, climbing into a limousine. Then it exploded.
Then I was in a library, with loads of friends. Suddenly, everything went red and sirens went off. Everyone began to panic as small, plastic fireworks flew through the windows, destroying bookshelves and killing people as they exploded. I managed to escape, getting into my Mum's car, after which she drove away.
As we arrived home, I got out of the car and hurried into the house. Then there was a loud explosion; the car had been destroyed, along with my Mum and sisters. Then their undead bodies entered the house in varying stages of mutilation.
Then I found a revolver and shot this guy in the face. He had an afro and big glasses. Apparently, he was a serial killer who specialised in plastic fireworks.
It was seriously the freakiest fucking nightmare I have EVER had, but it terrified me for weeks.