...The problem was not the teenagers, but the parents. Where were they? I don't think it's a bad thing for the parents to give them freedom, but maybe limited freedom would have been better.
If it were my kids, and a crowded show like Fantasmic, I would have been sitting nearby. It's one thing to let them go on Space Mountain, while mom and dad take younger sibling on Buzz Lightyear, but it is completely different to set kids loose for a 2 hour wait for Fantasmic.
Teenagers are easily tempted to play teenage pranks, but in a place where pranks can get them into serious trouble with strangers, and/or CMs, the parents would be wiser not to tempt them with freedom.