For this icebreaker, you will need to break your teens into groups of no more than seven, but no less than four.
BEFORE the teen meeting, and IN SECRET, recruit one teen for each group that will be the one who will disagree. That teen is instructed that NO MATTER WHAT, he is to do his best to make sure that the group does not reach a unified conclusion.

As the teens gather into the room, form them into groups (with one "disruptive" teen planted in each group) and tell them that you will be teaching on unity this evening. The first group to come up with an agreed-upon decision will each win a prize. Tell them the subject of discussion is two-minutes long, and the discussion is to be about uniforms on kids in public school. Start your stopwatch for two minutes.

This is WHAT WILL HAPPEN: While the team tries to arrive at a unified decision, your "planted" teen will do everything to disrupt by changing his mind. Even if the group agrees with his disagreement, he is to change his mind. You will see that discussion groups will get hostile toward the teen and even personal.

After the two minutes, blow the whistle and tell the whole youth group the scheme. Many of your teens will be embarrassed as they realise they got too personal when they should have been objective. Ask each of the "spy" teens how they were treated when they disagreed, and how the rest of the team felt about it.