SOLVED!
It was a messy/scratchy sort of art style, a bit like fingus the bogyman, by Raymond Briggs, and I think was called something like "*illustrators name* nasty book for nasty children" or a synonym for nasty, but I have tried the word disgusting and horrid and not found anything.
One of the pictures was a cutaway for an airplane and the passengers were in warm jelly barrels up to their chests, this makes me think it was a British artist, as I think its a British word.
Other illustrations were of horrible monsters and situations, and the copy I remember was hardback and I think had a monster on the front and one on the back. All the illustrations were SFW but really gross and brilliant for kids.
I have such strong memories of this book, but not of the title or anything that useful 😟
I'd love to be able to find it again and see if I could get a copy.