Lexi Sinclair posted about the incident on Facebook and said the day started off relaxing.
"While putting Christian's pool hat on, a woman (maybe mid 50's) comes up and makes conversation with me about Christian," wrote Sinclair.
Sinclair said the woman made small talk and asked how old her son was, how much he weighed and whether he slept well at night.
But then the conversation took a much more personal turn.
"She then proceeded to tell me that the men at the pool would feel more comfortable if I was in a one-piece swimsuit because a bikini isn't appropriate for a mother, especially one who's 'still recovering,'" wrote Sinclair.
Sinclair's first thought was to tell the woman off, but then she went with a more articulate response which is being called an epic smackdown online.
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"I just smiled, kissed my son and told her, 'I'm proud of my body. In just one year I've gained 50 pounds, and lost 37. I've grown a human and given birth to a beautiful miracle. My body provided food for my child. So, no, my body might not be the best sight for other men to see. My stretch marks and tummy pudge might not be sexy. But they're proof that I've done something amazing, and I have a man that loves me and finds me even sexier and more beautiful now.'"
As of Tuesday morning, Sinclair's message has been shared nearly 25,000 times on Facebook. Sinclair says the response has been mixed.
"Some people have told me, I should be prepared for the body shaming because it is disgusting," said Sinclair. "(However) I've gotten thousands of women telling me how much I've inspired them, which is awesome because all I was trying to do was share my experience with my friends and family and it ended up going way beyond that."
Thousands of women also wrote comments in support of Sinclair.
"You look awesome," wrote Jamie Williams Tull. "So proud of you for standing up to her stupidity! And shame on her."
While Ann Marie Stanton wrote, "You are beautiful. Screw what others think."
Another user, Honest Mum wrote, "You look amazing. It makes me so sad others feel the need to give their unsolicited opinion and police our choices. Keep being proud."