When Harry Met Sally... (1989), directed by Rob Reiner.
I've often confused three films I saw only once when they were new: this one, Sleepless in Seattle (1993) and You've Got Mail (1998).
All three star Meg Ryan.
Two star Tom Hanks (who would team with Ryan again in Joe Versus the Volcano (1990), although that is not likely to be confused with the others).
All three were written by Nora Ephron, who also directed two and produced two.
Rob Reiner directs one and appears in one.
I've rewatched them all recently and the first is still the best. Like most people I remember the cross country drive and the later "how to fake an orgasm" demo (they say a sign marks the spot in the restaurant now) but it has much more good stuff. Two people changing over the years, particularly Billy Crystal going from "a man can't be friends with a woman, he's always thinking about having sex with her", to actually having a woman as his best friend and then (O! the vicious irony) falling into bed with her and regretting it.
"Why can't people have sex with their friends?" asks the innocent free-thinker, to which anyone has been around for five minutes will respond with "DANGER! DANGER! It's trap! Don't go down there, fool!"
Great chemistry between Ryan and Crystal. Carrie Fisher and Bruno Kirby are the other couple.
I think Crystal gives a particularly fine performance here. Normally he has a smart-ass persona, but we see him grow out of that and become a better person. Watch him in the restaurant orgasm scene, his loving "ok, you got me" expression.
Appealing photography by Barry Sonnenfeld.
Available on Blu-ray with a lovely image.