Oftentimes they feel pretty horrible themselves, and retaliate against others for a sense of power and control.

That most certainly does not justify such treatment, though. Nobody should be harmed by anyone.

I guess that makes sense, although when I feel pretty horrible I just take it out on myself, as I really don't like causing other people grief. Although that unfortunately happens by accident sometimes anyway.

Some people are just.....well, evil. It's true. They just are.

There is a person in my class who is completely lacking in intelligence (and the ability to speak properly), who constantly tries to annoy and/or offend others.

Unfortunately, his methods (which involve making himself look like there is something seriously, mentally wrong with him) have gained him a reputation that causes people to either try to avoid him or say '*insert word of choice* off' the moment he comes near them, so that kind of prevents this from having much of an effect because there's only one person who actually talks to him. In fact, it's kind of sad, really. I find myself pitying him every now and then...

Same reason as ever, compensating for ones inadequacies. If someone's in a bad mood or feel threatened by someone innocent who appears better than them, they'll usually just lash out and try to make the other person feel as bad as they do. This goes for bullying, trolling or even the rather horrible term, "banter", as my group of friends like to put it.

As Chols said, many people lash out when they've been hurt themselves, but that doesn't justify anything.

Some people also don't know much else, which is generally caused by not-so-good parenting.

There's an idiom: misery loves company. Here's a question for you, when you're in a foul mood doesn't it make things 'better' when you make someone else feel the same way too?

Adding onto what has been said, for another reason people mistreat others: Oftentimes, someone will also feel a sense of superiority - even if they don't realize it - due to their background or belief.

Without actually stopping to consider the feelings of others, they will often assert this false sense of superiority by oppressing or degrading others due to their perceived inferiority, or will attempt to force others to change themselves so that they will meet their own strict standards and sense of moral superiority.

This type of thinking has lead to the downfall of many a society and unfortunately remains prevalent in our own today.

I for one find it extremely guilty to have others feel discomfort and/or pain from me. I'm a bit of a perfectionist and can't help feeling if everything isn't right, I have to deal with things and it's my fault.

It really depends on their personality I would think- I'm pretty compassionate/gentle. However some people probably have good qualities. I would like to think everybody does - it's whether or not they decide to show them or hide behind the mask of the ever-changing society.