3rdCoast-
Don't know about reddit or what is depicted in the HBO series, but there are some abuse backstories and parallel stories in the books. Some are explicit while others are merely alluded to.
Probably the most obvious abusive character is Joffrey. Sansa is ridiculed by Joff who, at one point in King's Landing, has one of his knights rip her dress and beat her in the castle courtyard. Joff also takes her up on the battlements to show her tarred heads on spikes, one of them being that of her own father.
Sandor Clegane was intentionally beaten and badly burned by his brother Gregor while they were children.
Brienne of Tarth is subjected to ridicule and a plot/bet from various knights as well as continual verbal abuse from Jaime Lannister. She is ridiculed behind her back for her unrequited juvenile affection for Renly.
When it comes to sexual abuse, there are plenty of instances. When it comes to siblings, the Lannisters aren't about to be shown up - Cersei abused Tyrion while he was an infant.
It should be plain that Varys is a eunuch but how he came to that condition is explicit in the books.
I don't know which book mentions this, but Craster supposedly sacrifices any male newborn in/at weirwood tree(s) to keep the Others/wights away from his keep. If you consider incest to be sexual abuse, Craster and Jaime are both pushing for first place in GoT.
One of the books goes in to why Tywin holds Tyrion in disdain - he thinks Tyrion caused his mother's death during childbirth. Tywin fails to see the shortcomings of Cersei and how Tyrion helped ensure that King's Landing would not fall to Stannis.
Speaking of Stannis, he mutilated Davos' hand. While this was done in the name of justice, we would label it cruel and unusual. He, based on Melisandre's fiery influence, wants to put to people to the flame for various reasons at various times.
There are numerous slights, neglects, abuses, manipulations and injuries in the books in greater or lesser degrees. It was medieval times.
Who thinks this stuff up? I think at some point the abuse themes in GoT is art imitating life.