Lee Dong-un portrays title character Young-bin, a handsome but obnoxious young man who begins the film by breaking off a relationship in a most impolite way: after waiting in a parked car so Young-bin won't get a ticket, the girlfriend reads him the riot act upon his return, prompting Young-bin to slip into the driver's seat, break up with her, and speed off, leaving his new ex-girlfriend stranded in the parking lot. From the get-go, Young-bin is not exactly a class act.
On the opposite side of the spectrum is the beautiful Ha-mi ,a meek university student looking for true love, but never seeming to find it. As is typical in this kind of film, the two meet purely by chance: Ha-mi accidentally text messages Young-bin before literally bumping into him. Ha-mi, feeling that their fortuitous meeting is a sign that they might be destined for one another, decides to pal around with Young-bin and see if there's any chemistry between them. Taken by Ha-mi's sincerity and her willingness to pick up the check, Young-bin jumps at the opportunity.
But Ha-mi's cousin, Chae-young (Shin Yi) isn't quite so enraptured with Young-bin and tries to dissuade Ha-mi from pursuing him. The thing is, Chae-young is a professional dating consultant and a strong subscriber to blood type personality theory. According to her, any relationship between the mismatched duo would be doomed to failure because Young-bin is a type-B male, which supposedly makes him arrogant, hardheaded, and generally a jerk, whereas Ha-mi is a type-A female, one who supposedly can't help being timid and obedient. But while Chae-young predicts impending doom, the happy couple try to give love a shot, ignoring their supposed blood type incompatibility.
