Re: Transmission Drain Plug
Tighten it enough and eventually it will fall out in your hand (followed quickly by all of your oil. lol).
Sounds stripped to me. You can pick up a somewhat universal "expanda-plug" at most parts stores. Insert plug, tighten bolt head with wrench, and the rubber sleeve expands to tightly fill the hole. Still will work as normal when you change fluid.
If it is indeed stripped to the point that you keep turning it and it will not tighten at all, I see this as your only option considering the size of the plug.