I love Hell. No one comic in particular, but the theme of eternal damnation and total depravity.
How about Attack on Titan?
At first, "Mai-chan's Daily Life" was what I considered to be most extreme, then the "-Kankan Hime/-Princess Violation" series was on my most extreme list. But as of now? Probably Uziga Waita's "Doku Doku Gravestone" is taking the cake.
Almost everything from Avatar/Boundless. Nothing is too disgusting for me.