The Withnail and I script is online (via Mountain*7). My favourite bit is right at the end when Withnail quotes Hamlet:
I have of late, but wherefore I know not, lost all my mirth and indeed it goes so heavily with my disposition that this goodly frame the earth seems to me a sterile promotory; this most excellent canopy the air, look you, this mighty o'rehanging firmament, this majestical roof fretted with golden fire; why, it appeareth nothing to me but a foul and pestilent congregation of vapours. What a piece of work is a man, how noble in reason, how infinite in faculties, how like an angel in aprehension, how like a God! The beauty of the world, paragon of animals; and yet to me, what is this quintessence of dusk. Man delights not me, no, nor women neither, nor women neither.