Exemple:
Man: 'After you, <em>ladies first</em>.'
Woman: 'Thank you!' 
Licence photo:
CC: Attribution, Commercial Use
Regionalism:
Neutral
Regional variant:
Neutral
Full Expression:
Etiquette: ladies first
Used by a man, usually when he holds a door open politely to allow a woman to go through first. This is still seen as polite behaviour by some, but other women do not like it as it makes them feel unequal.