Water usage is probably my biggest. Living in a high desert, my wife and MIL see no problem with filling one side of the sink with hot soapy water to wash a few dishes because “that’s just how I’ve always done it”, to watering the grass and plants for hours. All of this makes me mental.
People who believe in any religion are the same as dormant terrorist cells. One can have perfectly formal relationships with them on a daily basis, but given the right conditions, they become a huge, possibly lethal, risk.