Advances in automated detection of offensive language online, including hate speech and cyberbullying, require improved access to publicly available datasets comprising social media content. In this paper, we introduce BAN-PL, the first open dataset in the Polish language that encompasses texts flagged as harmful and subsequently removed by professional moderators. The dataset encompasses a total of 691,662 pieces of content from a popular social networking service, Wykop, often referred to as the "Polish Reddit", including both posts and comments, and is evenly distributed into two distinct classes: "harmful" and "neutral". We provide a comprehensive description of the data collection and preprocessing procedures, as well as highlight the linguistic specificity of the data. The BAN-PL dataset, along with advanced preprocessing scripts for, i.a., unmasking profanities, will be publicly available.