This will prevent David from sending you messages, friend request or from viewing your profile. They will not be notified. Comments on discussion boards from them will be hidden by default.
“Dear FB Friends, Fuck Facebook!!!!! — It has proven to be worthless as a book-selling device, and is nothing but a repository for perverts, reparation-seekers, old buddies looking for handouts, syphillitic ex-girlfriends looking for extra-curricular schlong and hack writers begging for blurbs.”
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James Ellroy