Some Kind of Wonderful (1987)

Synopsis

A young tomboy, Watts (Mary Stuart Masterson), finds her feelings for her best friend, Keith (Eric Stoltz), run deeper than just friendship when he gets a date with the most popular girl in school, Amanda, (Lea Thompson). Unfortunately, the girl's old boyfriend, Hardy (Craig Scheffer), who is from the rich section of town, is unable to let go of her, and plans to get back at Keith.