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Most of them probably have adult or parents as friends, and so fml helps them tell you about what trials they are going through, without letting the adults in on the secret. And I would rather see FML OMG then FUCKING DOUCHE IS A SHITHEAD. If it really bothered you, you would block them, or at least talk to them about it. And I don't think people know if you block them, I think it only affects you, and not them. So they should be able to see your stuff still.
I use it occassionally, but only when I mean it, you know? like the last time was when I logged onto my facebook after a year long hiatus to find this guy had asked me to coffee aftem meeting in a bookstore, but he had long since deleted his account so I couldnt take him up on his offer ): Definate FML moment, being honest.
And if you're familiar with star trek and the grouchy doctor Bones, then despite your dislike for FML I think youll still find his twitter amusing (: