These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Tomas Nau from A Deepness in the Sky and, apparently, the entire ruling class of Emergents. It seems like Thomas Nau in particular is trying to collect atrocities the way normal people collect stamps. Rape, genocide, and slavery are his favorites, and the he has all sorts of futuristic tools to help him with all three.
Flenser and Steel from A Fire Upon the Deep, although this only applies to the past Flenser — by the time Flenser appears in the story, he's partly a different person, due to the Tines being small-scale hive minds. It's complicated.
Moral Event Horizon: Tomas Nau: when we meet him he's already over the horizon by several million klicks — but it takes time for the truth to come out. If he hadn't already passed it before, we see several MEHs for him in text, but the biggest one is probably that he keeps Qiwi as a lover while still keeping around video footage of the time he raped and murdered her mother; then repeatedly allows her to find out about this and then wipes her memory of the event.