If I'm in a especially good mood, I'll try to keep the telemarketer on the phone as long as I can, seeming very interested in the product or service they are offering. When they get to the sale, I'll ask if the item comes in red. If it doesn't (and it doesn't), I'll get very enraged. They still won't hang up, because they think I really want the thing they're selling. Keeps them from bothering other folks and gives me some fun. Mostly I just ignore them with caller ID.