The plural possessive is "ladies'." "Lady" is singular, so if you were referring solely to one woman's shoes, it would be "the lady's shoes." As for your second question, I'm assuming you're referring to a group of women in your salutation of them, so it would be "Good morning, ladies." And as you're addressing them directly, the comma preceding "ladies" is necessary. I tried searching Google Ngram Viewer for "Look lady" and "Listen lady", both capitalized so as to occur at the start of a sentence, with the hope that these ngrams would reflect the usage of "lady" in a derogatory/dismissive sense. It seems to have come into usage around 1950, and really took off in the late 1990s.

Understanding the Context

etymology - "Look, lady", "Listen, lady" – lady as a pejorative ... single word requests - Is there an opposite gender for "lady ... Yes, milady comes from "my lady". Milady (from my lady) is an English term of address to a noble woman.

Key Insights

It is the female form of milord. And here's some background on milord: In the nineteenth century, milord (also milor) (pronounced "mee-lor") was well-known as a word which continental Europeans (especially French) whose jobs often brought them into contact with travellers (innkeepers, guides ... How did "lady" and "ladies" come to differ in conveying degree of respect? Does calling to a strange woman "Hey, lady!" sound angry? The takeaway from those is that you should generally avoid using the singular "lady" as a direct form of address to a person herself, as it's likely to sound confrontational.

Final Thoughts

There may be some exceptions... A lady or a woman? - English Language & Usage Stack Exchange The "fat lady" is the valkyrie Brünnhilde, who is traditionally presented as a very buxom lady with horned helmet, spear and round shield (although Amalie Materna played Brünnhilde during Wagner's lifetime (1876) with a winged helmet).