Oddly enough, it was an episode of "Little House on the Prairie" titled "Sylvia." A young girl, no older than 15, is raped by a 40+ man. I was no older than 13 myself, so it had a huge effect on me. I didn't completely understand it, but it made me much more respectful around girls my own age.
I'm kinda glad my first exposure to rape was unambiguously pro-victim. I wish more TV episodes addressed this issue. It would force writers to discuss the issue with some measure of sensitivity, instead of ceding it to films that are almost always unnecessarily graphic and sensational.
Don't worry, I'm stepping down from my soapbox now.