I hope you are asking about the case where your no is ignored or not valued and they continue to force you into doing something... I would like to remind you a few things about saying no...
1. Be polite
2. Be clear
3. Use the good opportunities you get to help others

Some other things you need to check is
1. Your friend circle.. If your friends are ignoring your values and the stands that you take on certain matters, you should question whether they are really a positive or a negative influence in your life... good friends don't force you to do things you do not want to do or judge on that basis...it is good to avoid such negative company as your walk with the Lord maybe hindered... i am not saying you should hate them, but don’t give an opportunity for them to change you in a bad manner...
2. Remember that people needn’t necessarily listen to you... that shouldn’t discourage us.. We should know why we take such stands and also that our identity isn’t defined by the way we are accepted by our friends... trust in the Lord and stick to doing the right thing...
3. If you feel the pressure is overwhelming and is really difficult for you to handle, please consider talking to a Believer friend or an elder for guidance and support...