I believe your alternator is burnt up, or to be exact, the rectification bridge inside.
The rectification bridge is an integrated part inside the alternator. It consists of multiple diodes that transform the AC voltages generated by the alternator windings to DC to supply the vehicle electricals and to charge the battery. These diodes are backward biased when battery is hooked up correctly and when the engine is not operating, therefore they draw no current from the battery. But they do become FORWARD biased when battery is hooked up backwards, and form a close circuit to the battery allowing HUGE current to flow, and resulting in instant destruction of the diodes themselves due to the massive heat generated.
Lesson I learned from you experience: Never leave idiots in the garage and go taking a dookie, take it right in front of them in the garage instead if they have to stay in.
Good luck.
