This guy needs to make better friends.
We're going to go out on a limb and say that this was a set up, if only because it's hard to believe that someone would be this horrible to their mate. Also, who just so happens to carry around a chain-less chainsaw, even if it's just to prank people? A sociopath, that's who.
And is it just us or does the prankee look really like BBC Radio 1's Chris Stark.