Roderick Russell was a bit shocked by just how personalized the ads on his Facebook page were becoming.

In the right-hand rail he started seeing messages for cures to a unique malady of his—he’s a professional sword swallower but has trouble swallowing his vitamin pills without gagging.

So this ad was a little too close to home: “Trouble swallowing pills? Does it seem ironic that swallowing swords is easy and then small pills make you gag?”

It seemed to be a case of Facebook knowing way too much about him, but how? He posted to the social network that he had just seen the “most targeted ad in the history of ad targeting.”

And it wasn’t the last. He received a series of increasingly personalized marketing messages that started to make him paranoid. It turned out, however, the ads were well-placed pranks by his roommate, Brian Swichkow, who used Facebook’s ad targeting tools called Custom Audiences to build a campaign geared to one person.