Definitions by Webster 57

Sister in flaw 

When your sister in law has Zero diving board skills.

My sister in flaw couldn't even front flip off the diving board

Sister in flaw by Webster 57 July 31, 2022

Sister in flaw 

When your sister in law thinks she has diving board skills and can't even pull off a front flip.

You should of seen my sister in flaw embarrass herself at our subdivision pool.

Sister in flaw by Webster 57 July 31, 2022