Czech Dark Humour

Was speaking with my Czech friends and they were talking about how Czech’s often have really dark humour. Making jokes about Jews, general racism, and sexism. They also said there are Czech jokes that shouldn’t be said out loud. I personally haven’t heard any types of jokes like this and the “dark” humour I have heard is more self-deprecating jokes. I come from the US so dark humour to me normally means jokes about slavery and the KKK. They said that those types of jokes were pretty light and not that dark here. Are there any jokes that accurately describe what they were talking about?