Ooh, You Make Me Sick (2005)

Young-eun, who works at a water purifier company, is hypocritical and totally selfish. For some reason Yong-hee, a dim-witted and over-friendly piano turner who works on the first floor, makes her uncomfortable and she tries to avoid him. But one day she tags along with Yong-hee when he makes house calls, and even manages to sell water purifiers to his clients. She continues to accompany him and take advantage of his help even though she finds him exasperating.