Two acerbic unemployed actors leave London for an inebriated holiday in the country. Hysterical, witty, drunken arguments occur. The cinematography, acting, screenplay and art direction are all brilliant. Endlessly quotable. There's a drinking game associated with this film; unfortunately, if you were to attempt to keep up with Withnail drink for drink (including the lighter fluid), you would surely die. Safety first. I watched it on the Criterion DVD, and you should, too. Sorry, you can't borrow mine. Brand new, it'll set you back around $50 on Ebay.
BTW, Bruce Robinson, the writer and director of this film, directs his first movie in 19 years with The Rum Diary out late 2011. It stars Johnny Depp, and is based on the Hunter S. Thompson novel.