Stress, failing relationships. poverty, illness, death, sorrow, self pity, anger, depression, unemployment, hunger, hormones, abuse, alcohol, drugs, criminal victimization, domestic violence, no money, heart break, no health insurance, poor or no housing, and other general tragedies of life. Not everyone can walk the good walk every day, no matter what they are facing privately. Usually mean behavior is about some kind of consuming inner pain. We need to apply compassion when others disppoint us.
I think people are operating under pressures and stresses we don't always understand. And what we think of as horrible and mean and rude may just seem like normal behaviour to some people, because they are so socially inept they don't understand that they are being mean. And then there are the mean people who do it on purpose....because it's fun.
Maybe they don't intend to be mean, it's just that they've got a sarcastic sense of humour.
Maybe you're not picking up on clues, or unable to understand what they want, and they get annoyed with you.
Have you considered, that if this always seems to happen to you, then maybe the problem is with YOU? Maybe you're being paranoid and over-sensitive, and seeing a problem where there is none. It's really hard to say, because you haven't given us any information, and your question is very self-serving.
Edit: Well played, sir.
1 might not know the reason bhind the "mean" attitude of the other...but there always is a reason to it!!
i noticed they did that to take a piece of your self esteem and add it to their own..
another reason is if you are a true Christian