A pepper is simply that, a fucking pepper. It is used to say hello, or wish someone good tidings. It can be used in conjunction with slepper and kapepper, all of which stem from pepper
When you get something that feels like it's stinging, burning, or itching your sphincter, that's a pepper. It could be from a leaky ass, a fart, or even after taking a poop. Sometimes orange grease (see orange grease) can be associated with this. It kind of feels like you have a pepper corn stuck in your sphincter.
Oh man I had spicy chili for lunch and now I have a pepper biting my ass.