Lisa may have forgotten her coral shoes, but Baby didn't forget to pack her rose-colored glasses for the trip to Kellerman's. The movie begins with a voice-over narration from Baby looking back at the past. We never hear her V.O. again, but the open lines do a perfect job of setting the tone.
BABY: That was the summer of 1963, when everybody called me "Baby" and it didn't occur to me to mind.
That one line says so much. It roots us in the time period, which even when the film was new in 1987, was still a nostalgic look at the past. It lets us know we're getting more than a typical '80s movie, with big shoulder pads and synthesizer music. This movie is going for something a little more timeless: the past filtered through present memory.
On top of that, the line tells us a lot about Baby's character. We know her name, we know it isn't her name, and we know at some point, probably during this movie, she is going to grow up.
So bam, all in that one line, we have the setting, characterization, foreshadowing, and the fact that this will be a coming of age story. The rest of the movie is told entirely through Baby's perspective, with a straight-through narrative, no flashbacks or time warps.