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.
This idea is also in the beta canon Star Trek novels. If I remember correctly, it was the Vanguard series with Carol Marcus and James Kirk dissolving their marriage.