In waifu threads, it definitely is being used as such and it's really pathetic.
Creating self insert characters
Aaron Torres
Caleb Young
make handbags out of
Carson Bell
This image makes me angry.
Thomas Ward
user is unironically the only good self-insert character in history of self-inserts.
Christian Cook
Adrian Rogers
Anonymous is a weird case.
Most people tend to hate self inserts because of their characteristics or being based off a real person, but Anonymous doesn't have either of that.
He's a non-descript Mannequin painted green for a Yea Forums flavor. he functions not as an insert, but for something for others to insert into. A generic character that generally tries not to stray from middle ground too far.
Similar. But different.
William Sullivan
Nah man
Levi Jenkins
Yeah usually a self-insert is one's very personal own creation, while user could be said he's more of a public domain. That might be enough for some people to separate the two and consider one acceptable.
I don't though, they both are so blatantly self-serving that I can't really care for either type of self-insert. Whenever I see user in art, I can feel the typical Yea Forums neet mouthbreathing on my back.