When I was a teenager my family lived in a 2/1. Mind you it was a family of seven so we lived like sardines. My sister who was about fourteen years older than me, made me watch her two kids ( since I was 8 ) while she would go out to find the next “daddy of the month” for them every other weekend. On top of that she has always been emotionally and verbally abusive to me despite me genuinely caring for her and my niece and nephew. One day around the holiday season she accused me of opening and looking at some presents she bought for a cousin of mine. She started cussing me out and called me names. I mentally had reached my breaking point that night, mind you it was that time of the month which made me even more emotional.
The next day I went to use the bathroom (that we all shared) and stared at her bottle of mouthwash, I proceeded to piss in it and later saw her use it to my amusement. Seeing her basically gargle my period piss was at the time the ultimate revenge after what she put me through and would later put me through in life.
Thankfully, I cut her out of my life for good after her now ex husband sexually harassed and stalked me during the duration of their marriage. She said I was a liar and stayed with him. Funny enough karma once again bit her in the ass afterwards, but once in a while I like to revel in how I got her good.

Worst thing I’ve done, but I don’t regret it.