I like my substance abuse surrounded by dry British humour (though I'm not really a fan of Trainspotting). Withnail & I is full of narcissism, paranoia and gleeful disobedience but also a sense of despair - an understanding this lifestyle is unsustainable and self-destructive - adding the pathos that makes a comedy last. You can tell it was based on real experiences (of the writer-director, Bruce Robinson, who hasn't done that many films, but I really need to check out How…