Strategy #1 - Be the Alpha Male and take control of your pack.
Verbally tell them to FUCK OFF. Be loud and clear and assertive. Do not disrepect, but don't be shy to curse if needed.
Do not show trebly anger in your voice or insecurity. Imagine you are training your dog. It's all in the energy you transmit and the tone of voice.
Be the alpha male.
If you look wimpy and nerdy and are not seen as the alpha male type, leader of the pack kind of thing, forget this strategy. They'll just laugh at you.
Strategy #2 - Highschool Revenge
Get them to perceive you as a psycho. If you are nerdy and quiet, use that to your advantange. You are the misterious type. You are kind of a freak, you might have decapitated bodies in your basement and human organs in your fridge. Get them to think that, and next time they bother you, act weird. Put a freaky grin in your face and tell them, "You are bothering me. Please Stop", and smile like a goblin, go back to your seat and start humming a child's song, or singing softly to some song with murderous lyrics.
Start bringing books on serial killers, and putting satanic screensaver and get a poster of that Postal Worker that went "postal", and / or one of the Unabomber. But don't be to obvious.
You could grab some random coworker and show him a pic of a decapitated body or something gross like that.
Make them think you have a stick on your shoulder. You were abused in Highschool, and waiting for the right time for Columbine style payback.
Strategy #3 - WAR WAR WAR
Start a war. You know the drill, bad taste dangerous office pranks that annoy the shit out of everyone.
This one won't help but It could be pretty fun while it lasts.
Strategy #4 - Direct approach
Go there and tell them something like "SHUT THE FUCK UP OR I'LL BUST YOUR HEAD OPEN".
Be sure to follow through your warning in case they don't shut up. You'd probably end up fired and arrested for assault. But you will become a legend. People will talk about you for years to come, and they will never fuck with you again.