- Fulfilled incestual relationships. One-sided ones are fine, even implied is okay, but when the series ends and the two siblings, cousins, or parent-child are post-coitus in bed...too far.
- Obviously pedophilia and the illusionary term hebephilia (Guess what? It's still pedophilia). However, this contrasts the Lolita-fetish adults where they are both adults and consensual (Konata's mother and father, various other examples) are fine. I'm actually a fan of the comedy trope where the mother or even grandmother looks ridiculously young.
- Shit like Maken-ki. Takes ecchi too far and in general is just gross. It's a very fine line between things like Queen's Blade and Qwaser (which are ultimately enjoyable) and this trash, but whatever it is that separates them makes a difference.
That would be the only things I find actively "unsettling or replusive." There are plenty of anime tropes I simply do not like and are a turn off or detrimental to the series, but they don't bother me.