"I don't exist—I happen."
What is the antiself? To explain, consider verbs. Some verbs have opposites. For example, "stand up" and "sit down". "Wake up" and "go to sleep". "The sun rises" and "the sun sets."
This means that "the sun rises" has two opposites: "The sun doesn't rise" or "The sun sets." One is abnegation; the other is an opposite or contrary action that is still an action—all on its own.
The antiself is not self-negation, or self-eradication, or the unself. If the self "happens"—if it's a verb—then it's got two opposites. The sun doesn't rise—I don't happen. The sun sets—the opposite of me happens.
Where this idea becomes poignant is if you don't like yourself.
If something about the sun rising displeases you, which would you prefer? "The sun doesn't rise"? Or, "the sun sets"?
If something about your self, which is happening, displeases you, would you prefer that "you" not happen? Or that "the opposite of you" do happen?
The latter happening is what I call the antiself. It's nothing more than a feeling. Much like I, as far as I can tell, am nothing more than a feeling.