Welp... if you personally ignore another user, and you don't want to assign antipoints to that user... couldn't you just not assign antipoints to that user? Or do you really need an extra mechanism to physically prevent you from giving antipoints to that user (a mechanism that still could be circumvented by simply unignoring that user)?

If you ignore a user, all of his/her posts will show up as hidden. You can still assign antipoints to hidden posts, though (yes, even without reading them, but the same goes for "regular" posts).
If you are ignored by another user, you can still read that other user's posts.