My first adult spanking was at a party given by a "punishment group." Punishments stung, but weren't severe. I went to the party as a guest of a woman I'd met online, a switch. At the time, I was a top only.
The party operated on the theory that someone had done something wrong, and was accused of so doing. The accuser made a case for guilt, the accused tried to explain. The group then voted on the guilt or innocence of the accused. I can't recall anyone ever being found innocent.
Since it was my first party, my first time with this group, I decided the easiest way to be accepted was to be accused of something. I was the first to be judged that afternoon. My friend came up with something to charge me with, I protested, I was found guilty. The judge, a woman holding a paddle, instructed me to approach the spanking bench. Once there, I was commanded to "drop trou." Yes - in front of a group of about 20 people, I bared my bottom and laid down on the bench.
I was given ten decent whacks with the paddle, and allowed to get up, get dressed, and return to my seat.
This wasn't the most painful spanking I've ever had, and was for years after the only one I received, but it was my entree to the local spanking community. I'd proved I was willing to take a spanking as well as given one. Because it opened so many doors for me, it was my most memorable, even though there have been several since that have come close and also are unforgettable.