Mum Brynne Huffman became an overnight hero. All because of her shorts.

When Brynne Huffman pulled on a pair of shorts on a hot Texas day, little did she know it would lead to her becoming an internet-famous champion of body positivity.

The 39-year-old mother of two has inspired the hashtag shortsonsaturday, encouraging women all over the world to bare their legs regardless of their shape or size.

Heroine indeed. Image: Facebook/Brynne Huffman

It all began with a stranger's snide comment while waiting in line at UPS last weekend.

In a now-viral Facebook post (it's attracted more than 11,000 likes and been shared more than 4800 times), Brynne told of how the person behind her complimented her hair, but told her she ought to "reconsider" her mid-thigh shorts.

Filled with rage, Brynne pleaded with her Facebook friends to shirk social pre-conceptions about body size and stop being hurtful to other women.

"You might have an issue with my body. I don't. And I've worked very hard past judgemental family and friends, past divorce, past depression to NOT have an issue with my body," she wrote.

"Women, do not tear each other down. Celebrate each other. Every day."

And celebrate they did.

Thousands of women commented on Brynne's post to express their support, prompting her to harness the positivity with the #shortsonsaturday campaign.

Here's how it works, she wrote in another Facebook post.

"Step 1: Get a pair of shorts. Buy a new pair or find a pair you own and like.
Step 2: Put on the shorts.
Step 3: Leave the house. Start small. Or go big.

And then...BE SUPPORTIVE. If you see someone else wearing shorts, tell them "love your shorts!" And if you see someone else being shamed, speak up."

Thanks to the overwhelming support, Brynne is well beyond the anger.

"I'm in a wonderful place now! The factors contributing to that are too numerous to count, but I'm lucky. It's been a journey," she told People.

"Your body is your business. Do not tear each other down. Put on your shorts and get out there."