'I already got titled a person who doesn't say 'No'.
Does it sound natural enough?
that formulation does not sound natural. "Titled" doesn't work. "Titled" as sounds even worse to my ear.
here are a few options that could work in North America. There are likely others as well.
He 's known as someone who can't say no.
They call him Mr. Can't Say No.
He's infamous as someone who can't say no.
Just call me Mr. Can't Say No.