Beginning with Lutheranism, it was their unwillingness to convert: https://en.wikipedia.org/wiki/Martin_Luther_and_antisemitism

Prior to Lutheranism it was their unwillingness to convert, see Spanish Inquisition: https://en.wikipedia.org/wiki/Spanish_Inquisition

If you're seeking some negative stereotype that's true about them, you'll be disappointed to find out that the main one was their unwillingness to convert.