A Miserable Fuck is someone who has had such a shitty life that no other phrase could possibly describe it. This kind of person has had so many shits taken in their happy meals that their life is just unbearable. Miserable Fucks typically can't get any pussy and stick to their books, they don't drive cars and ussually have other people drive them around. They don't hold a job, dress decently, or shave. They masturbate their (generally small) penis so frequently that even if they did get pussy it would fail to function by age 25.
Me: Hey man you wanna go to the have sex with beautiful lesbian women all night club? I'm paying.
Bro: Nah man I'm to busy masturbating my (generally small) penis extremely frequently.
Me: Dude, you're like a textbook definition of a Miserable Fuck