a flag previously used by the Ukrainian Insurgent Army (UPA) and the Bandera wing of the Organization of Ukrainian Nationalists (OUN), and now used by various Ukrainian nationalist organizations and parties, including UNA-UNSO, Right Sector, Congress of Ukrainian Nationalists and others.
In Poland, the red-and-black flag is widely associated with the Massacres of Poles in Volhynia and Eastern Galicia, during which between 60,000 and 120,000 Poles were murdered by the UPA.
horizontal vs diagonal makes a big difference here
https://en.m.wikipedia.org/wiki/Flag_of_the_Ukrainian_Insurgent_Army
https://en.m.wikipedia.org/wiki/Communist_symbolism#Red_and_black_flag