There are only a few movies I am capable of sitting through every single time I re-watch them, no matter how fidgety or distracted I am. And chief among them is my all-time favourite movie, Full Metal Jacket (1987).
I first saw it at the tender age of five, thanks to my father's lax parenting. I remember hiding behind the sofa when (26-year-old spoiler alert) Private Gomer Pyle (Vincent D'Onofrio) blew his brains out in the lavatory. But I was also fascinated by the incredible rantings of Gunnery Sergeant Hartman (R. Lee Ermey) and the (again, ancient spoiler alert) completely unexpected ending. As I grew older I understood more of the film and its impulses. It always seemed to be floating around, lying somewhere on the living room shelf/in a computer hard drive/school library video collection, and I could never resist watching it just one more time.
What I love about Full Metal Jacket is firstly, the quotability of the dialogue. The movie was inspired by Gustav Hasford's novel, The Short-Timers, which director Stanley Kubrick loved for its 'poetic... carved-out, stark quality' (thanks, Wikipedia). So Full Metal Jacket is a movie that moves around the rhythms of the dialogue, like a jazz score complete with genius improvisations - witness Hartman's famously ad-libbed threats and insults in his introductory scene, a solo virtuoso performance that blows everything else out of the water. Joker is the movie's bassline, a laconic presence thrumming with moral tension, while Private Pyle and his tragedy constitute the operatic climax reached in the first act of the movie.
Secondly, the depth is just amazing - it is a Kubrick production, after all, his attempt to show what war was like. Now, I've never been to war, or even to National Service (I have done my tiny, top-security bit to protect the nation, does that count?) but even I know that what Kubrick presents is not so much realism as a hyper-reality, a telling of the truth that bears only a half-resemblance to daily existence. Yet it's still the truth, and you know it. Yes, there are explosions, and people dying, and prostitution and misery, but someone like Animal Mother (Adam Baldwin) wouldn't really have a quote from the Bhagavad Gita inscribed on his helmet ("I am become death") because a real-life Animal Mother would have the reading level of an eight year old with severe ADHD. But all the same, he has become death. So it's true.
Lastly, the duality present in Full Metal Jacket is probably a topic that every film studies undergraduate has pulled together a half-baked essay on, but I'll contribute my thoughts all the same. As Joker wrestles with the "duality of man" (sample: "I wanted to meet interesting and stimulating people of an ancient culture... and kill them") he is surrounded by dual characters and themes ("inside every gook there is an American trying to get out"). The dehumanisation of the Marines in boot camp (beating Private Pyle under the cover of night) shines darkly against their grief and desperation at losing their friends to the mystery sniper. Private Pyle himself, a pale and wobbly contrast to Gunnery Sergeant Hartman's tough and leathery exterior, gains in physical strength and skill at the same time that Hartman softens up, complimenting his shooting and emphasising that "you are definitely born again hard!" (A lovely bit of irony - Pyle's rebirth is Hartman's death.)
My favourite duality involves the Saigon hooker ("Me love you long time! Me so hoooorny!"), about whom Joker makes a somewhat prescient remark: "Half these gook whores are serving officers in the Viet Cong, the other half have got TB. Be sure you only fuck the ones that cough." The prostitute's counterpart is the virginal teenage sniper, who takes on the role of the deadly aggressor until she is dispatched by Joker. While the prostitute sells her body to the Americans, the young female sniper uses her physicality to deal out death to them. Kubrick also piled on the irony by having Gunnery Sergeant Hartman brag about "what one motivated Marine and his rifle can do!" in the first movie's first half, then showing the devastating consequences of his boast in the second half - except it's done to the Marines, not by them.
A parting note: You know you've watched a movie too many times when you don't have to use IMDB to look up the quotes - and you still end up wasting time on YouTube re-watching all the scenes. The only other film I can do this for? Amy Heckerling's Clueless (1995). But that's another essay, for another time.