Easiest way to ruin a PC running XP

Just kinda curious what is the easiest way to fuck up someones computer? Im not exaclty a pro at this sort of thing but some jackass (which i also happen to know in person) has been sending crap to my email which my antivirus sez is harmful (i opened the first one on another computer (R.I.P), but he keeps sending stuff). What I would like to know is where he gets this stuff? And, is there a smart way to retaliate or should I just let him be?

(note: id prefer to be able to return the favor, but ill stick to whatever is a more sound decision)

um,... so in plain english, how is this done?

Are you >>1? Then grow the fuck up already.

Only a 13 year old jackass would think of this. Why not go out to the playground and get beaten up instead? This is pathetic.