Almost every female gym-goer will have experienced the same thing – the man who drapes his towel, his hoodie, his water bottle and himself all over the weights section, glaring at you if you dare to go anywhere near him.
Because what could you, a woman, really want with those weights?
Unfortunately, in many cases, this kind of "gymtimidation" goes much further, descending into threats, jeers and even physical violence. Female runners find themselves followed home, while women cyclists get their paths blocked.
A 2019 study by FitRated revealed that nearly three-quarters of women were being harassed at the gym on a regular basis, with one in five women cancelling their membership because they didn't like being stared at.
What's more, this kind of exercise aggression, typically perpetrated by a small minority of men towards women, appears to be on the rise.
The issue was brought to the nation's attention recently when Dr Josephine Perry, a sports psychologist and author, tweeted about a terrible experience in a swimming pool when she was attacked by a man she kept overtaking.
"Attacked in the pool this morning for overtaking a fragile male ego," she wrote.
"Grabbed my feet and held me underwater. Then starts yelling. Lifeguards lovely but of course it is me that has to leave as I can’t risk swimming with an aggressive man far stronger than I."
The man, who Dr Perry has reported to both the swimming pool and the police, also shouted aggressively at her and challenged her to a race. Her post has received more than 17.5k likes and counting, and prompted hundreds of other women to share their own stories of exercise aggression.
"These included women being swum into, pushed into lane ropes, intimidated into getting out of the pool and grabbed (as) I was," Dr Perry told Yahoo.
"I also heard stories from cyclists, runners, netballers, squash players and horse riders of receiving this kind of treatment when they were performing better than a male counterpart.
"A few men also got in touch to say they had been targeted too – especially those who were in wheelchairs, so others had assumed they wouldn’t be as fast as they actually are."
Children and teenagers also sometimes seem to be the victims of exercise aggression.
"I too have had my ankles grabbed after passing men in the pool, many an angry swimmer has felt the need to tug or hit me," former international swimmer Jane Copeland wrote recently in The Independent.
"As a child, the violence became part of the landscape. In public pools, it was all but expected."
While it's difficult to understand why anyone would behave in this manner, incidents often seem to happen when a man feels intimidated by the performance of a women, a child, or anyone else they consider should be "weaker" than them.
"I have no idea why someone would do this, but from the stories I heard it does seem to be that it happens more often when the female is faster, stronger or more skilled at the sport they are doing than the man," said Dr Perry.
So if you experience exercise aggression, what should you do? Firstly, if it's possible and safe to do so, it's really important to report any acts of aggression to gym or pool managements (and potentially the police).
Above all else, don't let it stop you exercising, or make you hold back in your performance.
"I am so keen this does not stop anyone exercising," said Dr Perry. "It is so important for our physical, mental and cognitive health.
"And we definitely should not hold back our performance – if we have worked hard to get faster, stronger or more skilled we should be proud of how good we have become.
"But what I would love to see us do is report every single case of aggression.
"So many women have become used to these constant aggressions we just move on, but this allows these few men to carry on, too – only when we report all of them will gyms and clubs and pools have to put in place policies and take action."
If we don't act now to stop women being mentally and physically intimidated during exercise, we risk undoing much of the brilliant work done by campaigns such as This Girl Can, which inspires all women, but especially younger women and girls, to shake off any fear of judgement around sport.
Dr Perry believes that if we support all children carefully from a young age we can work to prevent exercise aggression in the next generation.
"I would love to see more mixed PE sessions in schools, especially primary schools," she said.
"That way the 'Boys Are Better At Sport' attitude isn’t pushed from such a young age."
Watch: Serena Williams pelts a heckler with a tennis ball