Hands down -----> Immanuel Kant's Critique of Pure Reason
Bright guy, but a terrible writer. I only made it about 20 pages after reading the introduction before I gave up. The ideas are complex enough without having to deal with paragraph length sentences the whole time. His sentences have the nested story structure of 1001 Arabian Nights. For example:
"The same is the case with the internal intuition, not only because, in the internal intuition, the representation of the external senses constitutes the material with which the mind is occupied; but because time, in which we place, and which itself antecedes the consciousness of, these representations in experience, and which, as the formal condition of the mode according to which objects are placed in the mind, lies at the foundation of them, contains relations of the successive, the co-existant, and of that which always must be co-existent with succession, the permanent."
Fuck Kant (Edit: or, in all fairness to Kant, fuck the translator).
