If you want to screw with people using ads, one of the best ways to do it is to put "hidden text" in emails. Like I read about how one guy at a workplace kept complaining someone was stealing his mechanical pencil lead. So a coworker in every email he sent this guy, at the bottom would write "mechanical pencil" "pencil lead" and etc, and then change the font color to white, so you wouldn't see it. Google started showing all these ads for mechanical pencil lead on sale, and the guy went all tinfoil hat and "google is listening to my converstations".