SAOTOME SADISM #2

 Even were I reading RANMA in the original Japanese, I doubt I would see Rumiko Takahashi explain why Ranma acts like such a jerk, when he's actually a fairly compassionate guy. Since he's a Japanese kid who's been away from his home country for many years, mostly training in Chinese martial arts, the most believable explanations are that (a) he simply hasn't been around his peers very much and has not been well socialized, particularly in relationships with the opposite gender, and (b) he's so heavily invested in martial arts that he tends to see every conflict as a challenge.

So after his knowing Akane a few days, it's evident that he likes her and is attracted to her, but he acts toward her more like a bratty ten-year-old than a sixteen-year-old high schooler. He's smart enough to see that, even though a lot of boys pursue Akane, she's still very insecure about her appearance and her tomboy pursuits. So after Akane challenges him to a match-- a match Ranma could certainly win with skill alone-- he uses the fight as an excuse to pay her a compliment and watch her get flustered.

However, as clever as this gambit is, he shows incredible stupidity by intruding on Akane via her window-- not even to peep at her, but apparently just to see if she's internalized his compliment. And because he can't resist the temptation to taunt her again, he gets a well-deserved clobbering from her. 

To be sure, Ranma enjoys teasing victims, particularly his rival Ryoga, so Ranma's combative nature isn't confined to his romantic interests. Akane, for her part, never shows any desire to play games with people, and barely has any interest in proving her skills against antagonists. Ranma might be some sort of masochist, but Akane is only a sadist when she's forced into the role.