They had been "up" for a period of time, and Terry , who owned guns, was handling a pistol. Whomever it was that was with him was like, "Be careful with that thing." And Terry either dropped the clip out, or showed him that the clip had already been removed.
He says something like, "It's ok. See? The clip isn't in it." And then in a supposedly joking-around manner to indicate the gun was empty, he pointed it straight to his head and pulled the trigger. But there was still one in the chamber. He had ignored a very important rule of guns, possibly forgetting because of the partying, which is to treat all firearms as if they are loaded.
Tragic indeed, but totally and completely avoidable!