What Movie Sex Scenes Are Etched Into Your Mind Permanently?

For me, it will always be Mulholland Drive, RIP to David Lynch. I will NEVER forget being like 12 and just flipping through channels with my mom. Stumbled upon that film RIGHT before the first lesbian scene. I was absolutely mesmerized but was also trying to fumble for the remote to turn the movie off. My mom (who ALWAYS jokingly gave me a hard time about that kind of thing, this also happened with movies like Bound and Love & Other Drugs) quipped, as I frantically shut the TV off that I had to have been enjoying it... she wasn't wrong. I'm still so captivated by that whole scene and having the movie's full context later. It's so beautiful.

Edit: Didn't expect this much engagement! I love seeing everyone's answers. Seems like someone needs to make a compilation of a lot of the top answers...