If someone made a state-of-the-art sandwich..

[Psychotic]

Why would this diarrhoea be explosive?

To answer that we must look at what causes explosive diarrhea.

If you experience explosive diarrhea, first ask yourself if your diet may be responsible. Any increase in fruit, vegetable, bran cereal or whole grain consumption is putting more indigestible fiber into your gut, which acts to soften stool and speed the transit of fecal matter through the intestines. Excessive fiber, or a drastic increase in fiber intake, can cause gas and diarrhea, including explosive diarrhea. Fruits, vegetables and whole grains also contain some poorly digested starches and sugars

So you see, the sandwich which was, if you watch the scene, triple layered with cheap white bread and of course the assumed fruit content of the chutney itself will lead to poor digestion and increased gas.

Also, how can it possibly go through someone's digestive system, babyIMG_6989.JPG that quickly?

This is no ordinary sandwich. Remember that Lister invented the sandwich after reading a book on biological warfare. Remember that this is akin to "bowel surgery". Remember that Rimmer instantly said "I feel like I'm having a baby".

Vomiting I can understand

Instant vomiting eh

Instant vomiting... on the floor

Thus ruining the floor

Thus being concerned about the state of the floor is a natural state of affairs

Thus well well well you hamster cheeked scouse goit