What do you do when you meet people who are bent on making you sad or look bad?

Some times in life one meet people who are bent on making you feel miserable. I hate people who would like to make me feel streased. I met some people who tried anything possible to make the already bitter life of mine look more miserable again. I hate it when I am pissed while I am working and some one try to make it worse. I do pity the person, like this stupid student who who was bent on making me feel more unhappier. but I gave him what he deserved, and placed him in the right place. and this old man... too..... I honestly have had a bad experience of this country.