I gave him a medicine that works well for his sickly younger sister as a gift, since he keeps canceling dates using his sister as an excuse.

A story about giving a cure-all medicine to a shitty sister-in-law and intimidating and disciplining a shitty fiancé. The protagonist has a rather foul mouth and bad personality, but I don't think she's completely beyond saving. Rather, she tries to solve her own problems and does her best with what she can do, so this time it just became more severe. Probably. A convenient happy ending and schadenfreude are just thrown in for good measure. I'm also posting this on Alphapolis.