John Cusack, the Manic Pixie Dream Boy.
In this entire movie, Lloyd exists almost solely as a vehicle to make Diane happy. He's the perfect gentleman, a quirky nervous guy who'll make you laugh and cringe at once, and attempts grandiose romantic gestures, like of course the iconic boombox scene. He's got his own story arc trying to figure out his life, but really, no... this is Diane's story, and Lloyd is just there to help her along her own story arc.
I find it so interesting that, fifteen years before Nathan Rabin coined the term Manic Pixie Dream Girl, Lloyd Dobler was the ultimate example of that. And... I can't really fault the film for it, either, because he is such a dream boat, like damn.
An ultimate teen romantic comedy, even if I disagree with the clean-cut nicely-wrapped ending, because something messier would have been a lot more satisfying.