If you know that “to fuck” a person is to have sex with him/her, you automatically understand that a fuckable person is one that you would like to fuck. Accordingly is an unfuckable person a person that you don't want to fuck at all. A refuckable person is a person you would like to fuck again, while an unrefuckable person is one that you don't want to fuck again. You know the meaning of all these words by virtue of your knowledge of the individual morphemes fuck, re-, -able and un- and the rules for their combination.
A fuckbater is someone who tries to threaten or belittle someone but obviously doesn't pose a threat
Fuckbaters also tend to be pervy but in the telescope way and not the assault way
They are harmless, so you can still be their friend if you so choose
Other than being like this, they are pretty okay most of the time
Fuckbater: I'm gonna kill you if you don't give me that cool egg!
Person: This is my egg, you should learn how to hard boil eggs.
Fuckbater: I will hurt you now!!!! *he grabs them*
Person: Unhand me, you fuckbater.
Fuckbater: Gah! *He recoils in fear*