Anime can be as disturbing and gross as a Hollywood flick with insane amounts of Violence, Sadism, and down-right Disturbing stuff.
By no means this is an implication that these are bad Anime. Here is a concise list of all the Anime with horrendously disturbing and sickening themes whether they are good or bad is a personal preference and highly debatable.
These are quite possibly the Top 6 most SICKENING Anime ever.
Read ahead at your own discretion. You have been warned.