When you tell your friend you won't do something you don't feel good about, speak with conviction. Speak with sincerity. You'll be surprised. By asserting yourself honestly and firmly, you might gain respect and admiration from your peers. Remember you can always walk away and ignore them.
Actions sometimes speak louder than words.
Do it casually. Do it confidently. Remember, not all peer pressure is negative. Friends can lend a lot of positive support for each other too. Now Joseph had been taken down to Egypt.