Use 'detestable' to express strong negative emotions toward something or someone. Their detestable treatment of animals made her decide to leave the event.
Pro Tip 2/3
Intensity
'Detestable' shows a greater level of dislike than simply saying 'bad' or 'unpleasant'. The rotten smell in the room was absolutely detestable.
Pro Tip 3/3
Moral Judgment
'Detestable' often implies a moral or ethical condemnation of the subject. The politician's detestable actions were condemned by the public.