Unless your friends last name is Torvalds or Mitnick - it is very unlikely that he even knows how to do anything. Is it possible? Well, I mean, technically its possible, thats why big companies higher expensive people to protect the company - HalfLife 2 was delayed because valve was hacked for example - but if there is one thing you can be sure of, its that a home user wont be attacked like that directly no matter how mad you think some guy is at you. The onyl time stuff is worth while is when the profitablility outweighs the chance to go to jail. Like sending spam.
But then again, if he happens to have a virus on hand, and wants to use tor or something to prevent a direct link he could 'try stuff' and you can calmly remind him that his ISP tracks what he does and he could go to jail.