Facebook made me sad once when I was friends with a girl from school who I fancied. Fancied her from year 7 till I left after sixth form, and kept in touch.
One day, about 2 years after sixth form (so she's 20 at this point, as am I at same said point), she puts photos of her holiday in the Dominican Republic, and she's there in a bikini. Be still my beating heart, years of teenage wanton lust comes flooding back and I do what any lad would do, and I click the images.
The dream was ruined. Turns out she had a horrible, horrible tattoo that ran from her inner thigh all the way around her bum, back to her torso and up to her chest. Ruined whatever fantasies I had built up in my head over those 5 years.