The Guy Was Cool (2004) on Netflix

Plot summary

Han Ye-won is a cheerful, clumsy high school student; Ji Eun-sung is a hot-tempered vocational school student whom everyone knows as a bully. When Ye-won answers one of his rude notes on the school website, threatening phone calls start. Her friend Lee Kyung-won explains who Eun-sung is, and a text message orders Ye-won to meet him at the main gate. Ye-won and Kyung-won climb over the school wall to get away. Ye-won lands on Eun-sung on the far side, and their lips touch by accident. He shouts that she must take responsibility; a friend explains that Eun-sung has never held a girl's hand before, so the first girl to kiss him has to marry him. Ye-won turns down his invitation to his birthday party.