Users shouldn't be able to follow themselves

[AFCMS]

Probably the case for featured too, didn't check.

Frontend part prevent this at the moment, but it's obviously insufficient and require a backend check.

[AKArien]

While it is technically not ideal, there is a certain lack of need to do this, as it cannot happen during regular use of the website (which is to say, with the standard client) and doesn’t affect any other user, or even the user that does it.
I’m 50-50 between doing it, which would be simple, and not doing so, which would be simple in a different way, with both being effectively the same.