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.
I hate when people say that. I work in IT and that is a very popular phrase. Well you can do something wrong for a very long time.