Her bad habit is not only unmannerly, it potentially threatens your professional image.
From the post-gazette.com
Fantasy golf is the restrained, distant cousin of the other unmannerly, imaginary fantasy sports.
From the nytimes.com
They react with goodwill toward the unmannerly.
From the chron.com
As they made unmannerly plain a couple of centuries ago, most Americans do not admire Britain's parliamentary democracy, which is, after all, no panacea.
From the economist.com
Boards develop their own culture and conventions and mods need to do a lot of work to make sure they don't turn into a bear-pit where the juvenile and the ill-natured and the unmannerly rule.
From the guardian.co.uk
More examples
Ill-mannered: socially incorrect in behavior; "resentment flared at such an unmannered intrusion"