I'd briefly used k whilst learning to take a fist for the first time, but then I stopped using it.
Several years later, I dropped in on a FB mate whilst on my way home from work. He was in 'Tom of Finland' attire 😚 as he'd been playing earlier. We just chatted over a drink, but then my mate stood said he was tired and was going to bed for a few hours. He then said, that if I wanted to stay until he woke up, I was welcome to use the toys; lube; porn etc to 'entertain' myself. Before he went in to his bedroom, he added:
"Oh, there's a ready made slam on the side, you're welcome to it if you want!"
Whilst I was disappointed not to be playing with him, a slam in conjunction with the a toy and some porn, would make things enjoyable for me whilst on my own. Unfortunately, my FB had forgotten that he'd mixed k in with the slam. The result was I spent the next few hours, holding onto the sofa, wondering what the hell was happening. When my FB woke up, he realised instantly what had happened and was very apologetic.
He made it up to me afterwards 😉, but I've avoided k ever since.