Dan Pat Ppang (TV series 2004-2005)

Ga-ran and Nam-joon were classmates in elementary school. Ga-ran is a tomboy who prefers trousers to skirts, and loves taekwondo more than her piano lessons. Nam-joon on the other hand is Mr. Perfect who's got good looks, a fine brain, and is the most popular guy in school, especially among the girls. One day, Ga-ran sees Nam-joon giving away the sweet bun which Ga-ran's friend gave him, to another girl. Ga-ran throws herself at Nam-joon and beats him up, and their rivalry lasts throughout high school. A few years after college, Ga-ran and Nam-joon meet again as adults, both recovering from recent break-ups. Despite their constant bickering, they gradually realize that they're meant to be. - IMDb