Well in Utgarde Keep after the last boss, you take the shortcut out by jumping down the hole into the water...
Well if you're quicker than everyone you can mount up and jump, while in midair do your path of frost, and it will kill anyone who isn't already falling upon hitting the water.
To be safe you can just sit and wait while and before everyone flals through the second hole hit your path of frost, wait for them to die, turn it off, then float gracefully down.
It's a great laugh, and will definitely make someone be pissed off with you - all the more enjoyful.
Common sense, but not everyone knows it works in that manner. So go ahead and have fun.