People who shouldn't be on roofs at all frequently use them as runways for all sorts of mayhem. When I was a kid I used to toboggan off of my neighbour's barn and it was pretty fun and probably now illegal. However, if you are skittish, you may want to avoid your roof. Bad things happen when amateurs try to skate on shingles.
Now watch what happens when fear combines itself with peer pressure, alcohol, and a trampoline.