Pay 18% interest on a mortgage.
Fight in front of their kids. My childhood memories are flooded with my parents fighting, mom crying, dad verbally abusing her and my mom bitching about him to my sister and me. Really fucked up my childhood.
Never, ever talk about money/bills/finances in order to keep the kids from worrying.
I ended up financially illiterate when I left home, with no idea how much anything cost. Is $100 a month a lot for a phone bill? A good deal? How much is a week’s worth of groceries? I made a lot of avoidable mistakes.