The last time I took sexual harassment training, it was indicated that you were allowed to ask someone for a date once, and once only. If they said no, and you asked again, then it was harassment.
However, I would imagine that asking someone to star in a porn video would be sliiightly less well-received. Could you be sued for one incident? Probably not, but I wouldn't test my luck. Not at the office.
Random folks on the street? I doubt you'll be sued just for asking. But, if you're really worried about the legalities of making videos in your area, ask a lawyer.