Why do your co-workers pick on you? Why do they feel free to criticize and make fun of you instead of letting you work in peace?
You barely sit down at your desk when your co-workers start in on you: "Hey, look at those bags under your eyes. Wild weekend, huh?" or "There's donuts in the lunch room. Course you don't want any cause you're always on a diet." They borrow your stapler, take your pens, your scotch tape, your last clean whatever and never replace any of it no matter how nicely you ask. You're hurt and frustrated and near tears half the time, which only makes them meaner: "If you can't take the heat," they say, "Get out of the water!" You've tried telling your boss but he's always too busy to listen. You don't want to quit – what can you do?
People pick on people who are sensitive to it. Develop a second skin. Don't respond. Don't take the bait. Think of your favorite macho actor: Practice a Clint Eastwood dead-pan look. Look your tormentors right in the eye, stare at them for a moment and then say "You done? Good – I've got work to do," and turn back to your job.
Document your co-workers' demeaning comments. When you have half a page worth, show it to your boss and say: "Here's how my co-workers are interfering with my ability to do my job. They are wasting company time and decreasing my efficiency, which means wasting company dollars." Now your boss will listen to you, because now you've shown him a bottom line that matters - to him.