It's mean-spirited to leave nasty comments to someone.
Jenny is eating out at a restaurant and has to wait over an hour for her food.
Jenny wants to influence the restaurant to improve their service.
Jenny talks to the owner of the restaurant after the meal and suggests that hiring more waitstaff would make people more likely to want to come.
Jenny goes on Yelp and leaves a scathing review of the restaurant.
People hear about the improved service at the restaurant and start to patronize it more.
People see the bad review and decide not to go there, and it impacts the restaurant's business.