Very easily:
SSH into his Mac (if possible) or if he's already in, just type the following in a Terminal window and hit Enter:
That will SURELY turn off his sound (along with making everything else go byebye).
Seriously though, don't do it....it's just a joke but I know that sometimes people like that make you feel like performing the above command.
Have you brought it up to your superiors? Have the others join you in support and bring it to your administration's attention.
BTW, the HOW-TO section is for providing tips and tutorials on how to do things, not for requesting how to do something. I'm sure the mods will move it to the appropriate place, but just make sure you keep that in mind for future reference.