I've loved Haynes since Superstar, but never seen Poison, and I've got to admit I was slightly taken aback by Mark N's audacious choice of date movie.
It turned out to be a good thing, but I wouldn't necessarily recommend it on an ad hoc date basis - check whether the person you're interested in likes Foucault first. The film's made up of three inter-cut stories - Horror, Homo and Hero, shot in three genre delirious styles - 1950s sci-fi, queer cinema and documentary, with Genet credited as co-writer. The film looks at sexual stigmatization, debasement and perverse desire (or maybe desire made perverse), but manages to be very funny, touching in places, as well as pretty repulsive. The closing scene to Homo - a technicoloured flashback to the protagonists memory of a gang rape reenacted in spit and rose petals - has got to be one of the most disturbing I've ever seen.
Norman Bryson, Todd Haynes's Poison and Queer Cinema (spoiler warning)