Mean people are doing with their words what enemy soldiers do with their guns. They are dangerous and should be avoided. It would be good if you can find another job.
Nasty people are emotionally handicapped; they lack empathy. Try to find friends and talk to them about the nasty people you meet, in order to express your feeings.
To protect yourself: wonder what kind of nasty things they will invent today? Observe their behaviour, regard them as interesting phenomena to observe and investigate. Write date, time and what they did on a paper and save it for future use. There is also another method of protection: you might want to try the Paradox method. Each time they are nasty to you, play a game with them and thank them for their fine behavior- "oh thank you so much for your kind behavior..." But you need to be a good actor to carry this off. If you can, it will confuse them so much, perhaps they will leave you alone.