An old nickname created by JeremyPenner when he was young and foolish, which will haunt him for the rest of his natural life.
Back in the days before the Internet was popularized, there were BulletinBoardSystems. There was one BBS in particular that I frequented, known as the Programmer's Oasis. This was also the first BBS that I ever called. While exploring this BBS, I stumbled onto an exteremly popular door game known as Legend of the Red Dragon. It asked for a nickname. ArmpitMan was the first thing that popped into my head, and it made me giggle, so that's what I went with. At one point, I had resumes that pointed to my webpage as an accomplishment, the URL of which contained simply the word "Armpit," I believe. What potential employers thought of this, I don't know.
Pretty much everyone, at one point or other when I still used that nickname, would use deodorant on me as an attack, much like other people would be hit on the head with large trout. I never really understood this. I use deodorant on my armpits all the time, and they don't shrivel up and die. Armpits and deodorant go together.
There's at least one other ArmpitMan. I think he's an armpit fetishist. There used to be a site full of pictures of people's armpits. That's not me.
Several years later, I decided it was a rather childish name to be burdened with, and shortened it to "ApM". However, I was still instantly recognized as ArmpitMan by people I hadn't seen online in months. People who talk to me long enough will invariably ask what on earth it stands for. And so on. There's no use fighting it anymore.
Usually, when I sign up for something online, "armpitman" as a username is already taken. (Obviously this is with services that are popular enough that I don't even stand a chance of "apm".) This has led to me graduating to the more mature, "MrArmpitMan".