I admit I often get in trouble because I let myself get talked into going along with the crowd, even when I know what they're doing is wrong. Why can't I ever say no? I wish I wasn't such a weak person.
As you’ve discovered, going along with the crowd is seldom wise and will easily lead you astray (even if the “crowd” is only one other person). This is why the Bible bluntly warns, “Do not set foot on the path of the wicked or walk in the way of evildoers” (Proverbs 4:14).
Have you ever asked yourself why you give in so easily to the crowd’s pressure? Only you can answer this, of course, but I suspect the main reason is because you don’t want them to reject you or make fun of you. Instead, you want to be accepted and liked, and the best way to do this (you think) is to agree with them and go along with whatever they’re doing. To put it another way, you yearn for their friendship. But what kind of “friends” are they if they constantly get you in trouble and don’t care what happens to you?
Instead, I urge you to find a new friend — and that friend is Jesus. He loves you, and (unlike your present “friends”) He deeply cares what happens to you. He loves you so much that He gave His life for you, so you could be with Him in heaven forever. By a simple prayer of faith confess your sins to Him and ask Him to come into your life.
Then ask Him to help you find new friends — those who love Christ and will help you grow in your faith. Above all, make it your goal to please Christ, and not the crowd.