Let me make this blanket statement: Bullying is NEVER acceptable.
If you feel you are being bullied or have witnessed a case of bullying, please refer to your school's policy on bullying and contact an administrator. They are there to help.
In the meantime, here are some great resources that deal with the issue of bullying and ways to prevent it and help.
One great resource is StopBullying.gov. On this site are helpful articles and videos to educate people on the many forms of bullying and ways that you can prevent it.
Another great resource is pacerkidsagainstbullying.org. This is more of an interactive website which includes webisodes, games, and real-life stories that are all geared towards preventing bullying.
Remember, that it is always okay to talk to a trusted adult about any problems you may be facing. It is always easier to face things with others than standing alone.