Some of mine: Adorable trading symbols (like SEXI) or any business with a stadium. That popular prohibition worked well even pre-Enron Field.
I'm embarrassed by some of my simplistic rules, but they've saved me money. No retailing but only recently. Absolutely nothing Chinese. No banks. And my oldest one going back to my first stocks... no airlines.
Watching Robinhood, I think every rookie has to learn the airline "No Buy" rule for himself. Buffett knew that rule (US AIR) but had to learn it again at age 90.
______________________________________________________________ Because the Good Life is Just a Pump or Two Away