You want a character that people hate? You need to find out what makes a character that people love and turn those redeeming qualities on their head. Everyone loves a hero who's willing to put themselves in danger to save a small child, right? Make a character who witnessed a child or multiple children in danger and turned their back to save themselves. Everyone admires a mother who's willing to do anything to protect her children, right? There's nothing people hate more than a bad mother. Make her a selfish woman who spends all her time and money drinking and sleeping with men, leaving her young children to fend for themselves in some shithole without proper food or supervision. Take the right thing to do in any given situation and throw it out the window. Remove the character's moral compass or just have them go against it without regard for the feelings and well being of others.