I'm active at WP:AE, the arbitration enforcement noticeboard. This is a FAQ in which I try to answer questions that occasionally come up.

Please block or ban this or that editor, they are doing terrible things!

Please make a report about it at WP:AE in the form recommended there with all required information. Sorry for the hassle, but this ensures that we have all information we need to be able to act on your request and that the other user has an opportunity to respond to the request.

Somebody (or you!) threatened me with arbitration enforcement, but I didn't do anything wrong!

If you received a message like this one, you don't need to do anything. This is an informative message that any editor who is active in certain topic areas may receive. It is to inform you that that there are heightened expectations about user conduct regarding editing in such topic areas. The message doesn't mean that you did anything wrong, or that you are about to be blocked or banned. You may still want to read the pages it links to, though.

Please undo the arbitration enforcement block or ban you made!

Are you the editor who I banned or blocked?

Yes!
All right, please tell me why you disagree with my action and we'll see if we can reach an agreement. If you can't reach me on my talk page because you are blocked, please notify me by writing "{{ping|Sandstein}} ~~~~" on your talk page and I will respond there. You should read WP:GAB beforehand, though; it describes what administrators usually look for in such requests.
If I don't agree to undo my block or ban, you can appeal it. Please see Wikipedia:Arbitration Committee/Discretionary sanctions#Appeals and modifications for how to do this. If you cannot edit the forum of your choice because you are blocked, you can ping me, as described above, or another admin by writing {{adminhelp}} on your talk page, and they or I will copy your appeal to the forum of your choice.
No!
Please voice your concerns on my talk page. I'll try to address them as best I can as long as you assume good faith on my part and on that of others involved in the enforcement process. However, I'm likely not going to enter into a long discussion with you about whether the enforcement action was right or not. That's because our rules say that only the sanctioned editor, and not others, can appeal an AE sanction. If they choose not to appeal, they in effect accept the sanction – even if they say otherwise – and it is therefore moot to discuss the sanction further.
But you blocked or banned without a consensus / against consensus of other users or admins! That's wrong!

It isn't. The arbitration process is intended to result in binding solutions to conduct problems in circumstances where the normal consensus-based dispute resolution processes no longer work. That's why the Arbitration Committee has established rules for arbitration enforcement that make clear that "administrators do not need explicit consensus to enforce arbitration decisions and can always act unilaterally." They are encouraged, however, to seek input from other admins in unclear cases, and they may overrule a consensus of other admins, but only with caution.

Only if and when the sanctioned user makes an appeal does consensus come into play. The result of an appeal is dependent on consensus among the people reviewing the appeal, as described in the rules for appeals.