* {{Adorkable}}: Marwood can't stop nervously smiling, and Withnail is just ''so'' proud of finding one potato.
* AlternativeCharacterInterpretation:
** Is Withnail a drunken, vicious boor willing to throw his only friend under the bus or a conflicted, depressed actor with genuine talent who was abandoned by his family and developed a substance abuse problem?
** Is Marwood a sympathetic young working-class man trying to make it in a predominantly upper-class business or a racist homophobe?
** Is Monty a tragic figure suffering due to his closetedness or a lecherous attempted rapist?
* CultClassic: Universally considered one of the quintessential examples of the '80s.
* EnsembleDarkhorse:
** Danny the Dealer is such a memorable character that it's easy to forget that he's only in two scenes.
** Presuming Ed also makes a strong impression without even having any actual lines, even though Danny credits him with the "We have failed to paint it black" observation.
* HarsherInHindsight:
** Withnail was originally to be depicted committing suicide at the end. Vivian [=MacKerrell=], on whom he was based, died at only 50, due to throat cancer most likely caused by self-destructive behavior of some sort.
** Withnail is shown drinking lighter fluid, to Marwood's dismay. The real-life person he was based on died of throat cancer (nearly ten years after the movie came out), which the scriptwriter, who based Marwood on himself, blamed on the time he actually did drink lighter fluid.
** In a last-ditch effort to avoid a fight with the Irishman, Withnail says, "My wife is having a baby". During filming, Creator/RichardEGrant's wife suffered a miscarriage.
* HeartwarmingInHindsight: Withnail's boast about how's he gonna be a fucking star is tragic for the character, but triumphant for Creator/RichardEGrant, as he was essentially nobody when he landed the role which made him famous.
* HoYay:
** Made canon by Withnail getting "carried away" when he told Monty that Marwood was a "toilet trader" who was in love with him.
** See also: Marwood's [[NoSenseOfPersonalSpace constant violation]] of Withnail's personal space, the tendency for the two of them to call one another "luvvie", although that's probably down to the out-of-worker stereotype in England (which is queer coded to some extent) and Withnail's insistence, in the interest of their "safety", that they share a bed.
** Incidentally, Danny remarks that Marwood is "looking very beautiful" when he sees him emerging half-dressed from the bathroom.
** There's a shot after Marwood first refuses to let Withnail sleep in the same bed as him where the camera lingers a little on Withnail's face, almost entirely obscured by darkness, which suggests a sort of dejection.
* JerkassWoobie:
** Withnail towards the end, especially with his heartbreaking, awesomely spoken [[Theatre/{{Hamlet}} "What piece of work is a man"]] speech, with only the wolves to see it. Overall, there's a sense that the character has wasted his potential, possibly due to personal problems (he mentions his family hate him being on stage), and is externalising his own bitterness by making things miserable for everyone else.
** Monty tries to rape Marwood and makes him very uncomfortable beforehand, but is so deeply lonely and tragic that even Marwood feels sorry for him. He also gets some of the few poetic lines outside of Marwood's inner narration, and his speculation on beauty and decay is quite melancholy, as is his plea for Marwood, who he believes to be gay, not to waste his youth trying to deny himself as he "almost did". The Sexual Offenses Act had only been passed in the U.K two years before 1969: to some extent, Monty is around to see a new generation take advantage of freedoms he never had.
* MemeticMutation: The film is a virus that attacks the receptive mind, usually male and/or in higher education, leading to groups of people in pubs quoting the script at each other.
* NauseaFuel: Withnail and Marwood's kitchen. They haven't done the washing up for so long that the pile of dirty plates in their sink has things living in it.
* OneSceneWonder: The cop who screams "GET IN THE BACK OF THE VAN!"
* PeripheryDemographic: Both Creator/PaulMcGann and Creator/RichardEGrant have played [[Series/DoctorWho the Doctor]] -- the Eighth and [[WebAnimation/ScreamOfTheShalka alternative Ninth]], respectively. (Richard E. Grant also appeared as the Doctor in a [[Recap/DoctorWhoTheCurseOfFatalDeath rather infamous spoof]] and as Doctor Simeon/The Great Intelligence in [[Recap/DoctorWho2012CSTheSnowmen "The Snowmen"]] as well.) By sheer coincidence, these two regenerations of the Doctor were the first ones to be portrayed as overtly bisexual. Needless to say, the ''Series/DoctorWho'' slash fandom is all over ''Film/WithnailAndI''.
* PortmanteauCoupleName: Withwood for Withnail/Marwood.
* SpecialEffectsFailure: Occasionally, the sixties illusion is spoiled by the appearance of [[AnachronismStew 1980s automobiles]] in the background during certain shots.
* VindicatedByHistory: ScrewedByTheNetwork and ignored in the cinema, Robinson said "Thank Christ for VHS and [[VindicatedByCable late-night TV]]" for making the film a cult classic.
* TheWoobie: Marwood for most of the film. His first scene, more or less, is him having a panic attack, Withnail is sick on his boots, he gets threatened by a large Ulsterman, inducing another panic attack, gets creeped on by Monty and then has to drive all the way up to the Lake District with a drunken, belligerent Withnail next to him. And that's all just in the first half an hour or so of the film.
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