lol, Hey, I really appreciate that Bensin, I've watched Predator maybe, 5 times in the last couple weeks, ever since I went to see Predators (and I know you don't approve, but I enjoyed it). It's really a classic film, and unfortunately I don't think anything that comes out will come close.
Back on topic, though, I'm pretty sure the laugh at the end is JUST Sonny Landham (Billy), and not any other samples or actors or anything like that. Director probably said, "ok, do your big laugh, but at the end, lose it a little bit, go crazy." Because you hear Billy's laugh at least a few times throughout the film: "Strap this on your SORE-ASS Blain," "Get it? It was... cuz of the echo..." and lastly, "Do you think you could've found somethin' bigger?" They all sound distinctly the same, and the laugh at the end sames quite similar, as far as I can tell.
Another way to tell it's the Predator mimicking the human's voices, if you listen to the laugh at the very end, during the countdown, when he STARTS laughing, it sounds just a little off. By the time he takes that breath and lets loose again, it sounds EXACTLY like Billy. And by the end, he's gone crazy and I think maybe Anytime realizes what laughter really means and is really enjoying his last moments knowing Dutch is going down with him.
Straight cold playa.