Teens, for the love of God, if you're the experimental type (as I, fortunately and unfortunately were), make sure that you understand that the phrase "the safety word is...", especially when being handcuffed by an attractive but INSANE girl, usually comes right before A LOT OF PAIN.
You can discover that you have quite a lot of tolerance, but as soon as the cat o' nine tails or branding iron is brought out, flee.
Masochists: Please stop assuming that we sadists are into the same jazz as YOU.
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That prologue aside...
I was sixteen and had been dating this incredibly attractive (skinny, petite, extremely cute face) COOCOO FOR COCOPUFFS girl for about a couple of weeks, when she decides to kick things up a notch. Before that fateful night, our sexual escapades usually consisted of lots of biting, choking, scratching, hair pulling, hitting, handcuffs, soft-leather horsewhips, etc.
Well, that night she asked me, off of our experiences, if I was really into S&M. I told her I really didn't know, but I was starting to like bits and pieces of it.
In hindsight, I probably should've told her I was liking the S part a HELL of a lot better than the M.
After some foreplay, she used a different brand of handcuffs (later I came to find out that "different" meant cold, hard, and REAL) than normal and cuffed me to these shackle hooks. To this day, I despise her liberal parents for those fucking hoooks.
Given the prologue, I'm sure you can fill in the rest of the details.
[Point of interest: I've actually grown to like my happy face ass-brand, and the fiancee just finds it downright hilarious]