It is not that they do crazy things they do not know how to deal with stress. It is more likely for a teen to make a "bad" decision when they are under stress. Teens' brains are not yet developed; your brain is fully develop around the age of 25. That is why an adult will response better under stress than a teen.
"When reading emotion, teens (the picture up) rely more on the amygdala, while adults (The picture below) rely more on the frontal cortex." (Spinks, Sarah. "One Reason Teens Respond Differently To The World." PBS. PBS, 2002. Web. 19 Mar. 2012. <http://www.pbs.org/wgbh/pages/frontline/shows/teenbrain/work/onereason.html>.)
The links below explains a little more about the Frontal Cortex.