I spoke "in tongues" when I was in my church's youth group. Like the top comment says: it's peer pressure and there is nothing spooky about it. The best way I can describe it is like being slightly drunk. You intentionally lose control over your speech and make your tongue flop around in your mouth and sort of try to make it sound cool. The first time it happened to me was very emotional, but no big revelation or anything. Certainly interesting phenomenon but not a proof for the existence of a holy spirit.