Last week, Michelle Kirk, 28, of Fort Lauderdale, Florida, was one mile into a three-mile run when a man on a recumbent bike stopped her. She thought he was going to make small talk, but instead, he offered some unsolicited advice.

“He was like, ‘Not for nothing, but you need a new sports bra. Your boobs are really sagging and if you keep on running, the muscle fibers in your breasts are going to break down and your boobs are going to sag even more,’” Kirk told Runner’s World by phone. “And then he tells me how they’re going to head even further south than they are now. My jaw dropped. I was completely caught off guard.”

Kirk had her 18-month-old daughter with her in a stroller, so she didn’t want to get into an argument, and she was a little worried about their safety.

“He acted like by him seeing me, I ruined his whole day,” Kirk said. “If it really bothered him that much, he could have just looked away. But no, he came and confronted me, like he wanted a reaction from me.”

She told him all of her other sports bras were in the laundry, and then continued on with her run, fuming. She called a friend, who advised her not to go back and confront him. Instead, she used her anger to fuel the remainder of her run, which she ran faster than usual.

Kirk does interval training, and during one of her walk breaks, she stopped to post about her experience on Facebook, saying what she wished she could have said to the man directly.

The following post contains strong language. 

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She posted on her own page, and also posted it to the A Year of Running Facebook group, hoping to inspire some others. Her phone quickly lit up, as she started receiving likes and comments from people all over the world. The post went viral.

“I’ve gotten a lot of personal stories from people. This one guy, the first day after I posted it, he told me how he lost a lot of weight and how he struggles with different insecurities with his body and how after I posted that, it helped him see himself in a new light,” Kirk said. “That’s exactly what I was going for. I wanted people to see their self worth and their beauty. The fact that I was able to touch even just one person, my mission was accomplished.”

Kirk took up running not long before she got pregnant with her 18-month-old daughter. During her pregnancy, her doctor advised her that her heart rate was getting too high while she was running, and that she should stop exercising altogether. She did, and she gained nearly 80 pounds over the course of her pregnancy.

After her daughter was born, Kirk signed up for her first marathon, the 2016 Disney Marathon, which she completed the month her daughter turned one. Now she’s training to run November’s New York City Marathon. Since the birth of her daughter, Kirk has lost 100 pounds.

Having developed breasts relatively early in life, Kirk said that she was then very self-conscious about them.

“[This] brought up past feelings, especially the moment he said it…” Kirk said. “But it doesn’t bother me because I’m at the age now where I do accept myself and I love myself. I’m not going to let [something like this] ruin my day.”