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.
Nausea Fuel: Considering the point of the show, it's to be expected, but...
Hands-down, the most disgusting one ever was the tail end of the horse scene in Jackass Number Two — a scene so bad that it made a crew member vomit on set. Chris Pontius drinks horse semen. It was even blurred out in the theatrical version. There, now do you still wish you wanted to know that?
Jackass 2.5 reveals they also splashed it on a cameraman. The container was washed out and replaced with water, mind you, but it still disgusted the rest of the crew.
Dave England shits on a toy house toilet, gets the same reaction of disgust. The cameraman dry retches rather painfully.
The poo volcano in Jackass 3D, which is about as shitty as it sounds.
The climax of Jackass 3D — Steve-O is strapped into a porta-potty filled with all kinds of shit (literally) and flung high into the air. The cameras get covered in shit, there's a shit shower, it was so disgusting that nearly everyone puked..
The Sweatsuit Cocktail. Preston works out vigorously while wrapped in plastic wrap, and his resulting sweat (taken lovingly from his crotch and ass crack) is funneled into a cup. Which Steve-O then drinks. Remember Lance Bangs, the man who vomited during England's poop-encrusted adventures with a hardware store, a dollhouse, and during the horse scene? This scene causes Lance to throw up on his own camera.
England eats the ingredients of an omelet, then proceeds to vomit it back up. He then takes said vomit and cooks an omelet, which he eats. During the segment, Johnny Knoxville wears a Hazmat Suit. It's for humor value, but you kind of get where he's coming from.