I'm sorry, but people who bully others disgust me. It's not the people who are bullied are weak, it's the people bullying them who are the weak ones, an they know that. I did know someone who is bullied by a certain group of people. They verbally abused him, called him stupid and very, vulgar names. Well, one day, I became truly sickened by their acts and stood up for the boy. The group backed down, but continued their cruel ways the following day, sadly. I told the boy not to listen to them, and that the chances of seeing them later in life are slim. Just because he was different, they verbally bullied him (and probably still are) and tended to avoid him because he as "weird."
Being different is not a bad thing. Variety is something to be cherished; if everyone as the same, the world would be very strange. Just because someone thinks and/or acts different than you, doesn't give you an excuse to bullying that person.
If someone does bully you, never, ever use violence against them. As tempting as it may be, you may look like a bully too, even if that person has been bullying you for years. You're both still human with feelings. <3
Anyways, what would I do if I saw someone being bullied?
Simply, I'd stand up to the bully. There's no reason to knock someone down or lower one's self esteem because they don't wear the same clothes as you, or they listen to different music. We're all humans, and no one is better than one another.
I personally think the reason many people do not stand up to bullies is because of the threat of being bullied afterwards, or possibly being humiliated, etc. I am strongly against bullying. I find it pointless, and truly idiotic.