Unmannerly
/ʌnˈmænərli/
Definition 1 of 1
Pro Tip 1/3Social Situations
Use 'unmannerly' when someone acts inappropriately in social settings, breaking accepted social norms. 
Speaking with your mouth full is considered unmannerly.
Pro Tip 2/3Cultural Sensitivity
'Unmannerly' can reflect cultural expectations; what's rude in one culture may not be in another. 
Refusing food at a dinner may come off as unmannerly in some cultures.
Pro Tip 3/3Severity of Rudeness
'Unmannerly' often implies a lighter form of rudeness, not as harsh as insults or offensive language. 
Not thanking someone for a gift might be seen as unmannerly.