::SPOILERS::
I'm too disgusted to list all the idiotic things they did, but the fact that they didn't at least tie up the guy with the handy rope he brought, after they smothered him with the plastic, was the last straw. My husband made me change the channel because he was so pissed at these moronic characters.
You are not alone arteemus in your thinking. I kept saying it over and over while watching that they were so stupid I kept thinking, why not tie him up? There were many scenes throughout that were the same way, but that particular scene that you mention is the most glaring and memorable in its stupidity! (or should I say theirs!).
First of all, why they would pick up a man on the road is the most utterly ridiculous thing ever. Then they don't even lock the door of their motel room and they allow this guy to just walk in. Then the whole thing at the pool and the way they spoke in front of him in general. The kicker is how all of these girls have no compunction about accepting a "homemade" drink from this guy they don't know at all. There were scenes where guns were left behind or thrown down they could have used. Why they allowed the guy to just say Oh, the repair guy took my truck first; he'll come back. Would you accept this crap? No way! Can you be any more dense??????????? The cops were just as stupid, but these women set back women 200 years!