I was recently tricked into friending someone on Facebook. Someone created an account on Facebook with the same name as a current friend, but with a minor misspelling. Then they tried to friend me. I was busy and despite a small alarm bell in my head going off as I thought, “Aren't I already friends with them?” I still clicked confirm.
Whoops. Fortunately the real friend discovered the problem early and reported it to Facebook Abuse. Facebook responded promptly by disabling the fake account and little harm was done.