My SO's sister is a lesbian, a drama loving thunder-cunt of a lesbian. Always making plans, backing out at the last minute, numerous incidents; the list is a long one.
I told my SO I didn't like her sister, but I'll make an effort to get a long - at least long enough for the occasional visit.
So this one day, we were out of weed and my SO started calling around - the only person who could find any was her sister, ugh. I said I'd rather not buy any then get it from her, because only God knows the drama it'd start by potentially buying illegal narcotics off her sister; but my SO pitched a fit so I caved.
An hour later, we're at her sister's house - she left with our money, and had already came back. By all accounts, this was smooth. We rolled a joint and smoked it, then got up to leave.
I get out in the car, we can't find the weed anywhere. We looked everywhere, on the couch, all outside, even in the trash. It just "mysteriously" disappeared - which threw me into outrage mode. I was convinced they stole it. I told them cunts "I'm glad it only took $35 to show us who you really are; some lying, theiving, cunts. You can keep the weed, lose my number." then I started to drive away. My SO couldn't stand the idea of leaving things like that, so she hopped out the car. I told her if she was going to stay, STAY - I want nothing to do with these people. And I left.
I get home, still pretty mad. Open the car door... and there it is. Somehow, on the passenger floorboard is the baggie full of weed. I'm like... no fucking way.
So I pull out my phone thinking how I'm going to apologize for saying this awful heinious shit - when my SO texts me "I'm so sorry my sister stole from you. We'll never go back over there again, I promise. I'm so sorry.".
It was just too good. I mean seriously this is all I've ever wanted - to never have to spend time with her sister again, ever. And here it is, the perfect opportunity.
I put my phone back in my pocket, went upstairs and smoke a fat blunt all to myself. Then put everything a hour or so before my SO got back, never telling her I found the weed in my car.
This caused unbelievable strife between my SO and her sister, and their Mom. Their mom didn't know we smoked pot, and was outraged when she found out (it's unclear who told her) - which turned into her calling the police and all sorts of add-on drama, lesbian SO breaking up with her, and ultimately a complete loss in trust between my SO and her sister. And my SO's Mom refusing to talk to either of us because we were now known as some sort of "druggies".
So basically I set off a nuclear bomb in my SO's family, got safely away from the fallout- then watched them all burn.
For the next 3 years we dated, I only had to interact with her family maybe 3 times. So I still consider this lie worth it, but only barely.