Hmmm.
For Arnulf it's the fallen Matari.
Most of the ex members of Du'uma Fisi for the murder of all those liberated slaves. Eran for joining the Crusade. Scagga was a favourite back in the day, along with the female character whose name I can't currently recall who left U'K to join his organisation.
Also the people he considers to be truly toxic ideologically. Prominent Sansha, Blooders and EoM types tend to rattle his cage a tad.
Oddly he opposes the Imperials, but can see where they are coming from. He just disagrees with them. Hatred doesn't enter into it.