It is highly likely, that you either end up with a 2d character OR a character that people do not actually hate (or dislike).
Look at it this way:
If we (the readers) understand a character's motives and background, we are way more likely to relate to or at least understand (maybe even defend) that character's actions - Even if these actions are perceived as 'bad'...
So, if we do not get insight into what lies behind the character's actions, we are more likely to simply perceive that character as bad/evil...
Therefore, when you talk about this character being 'an asshole', have you yourself worked out why?
Of course, every person/character is unique, but if they do not 'suffer from' some disorder that makes you lack empathy, you most likely try to be a good person or treat people well - UNLESS they've been treated in a certain way, or have experienced some traumas.
In reality, there are close to infinite reasons why someone becomes an asshole... If you want your character to be authentic, they should have a reason for being it.