Of course black cats are unlucky..if you are a mouse!
My Mom is of Gypsy blood so she has to be the most superstitious person in history. I remember as a kid I missed out on seeing a total eclipse because that was a time demons came out to play....
Mind you, we had three black cats over the years, Sooty being the most recent who lived to 22 years of age, so there are some things she was not concerned with.
Ones that freaked her out were;
Putting shoes on a table. Found that one out when I took my new sneakers out of the box and placed them next to the box on the table. Apparently it was OK whilst they were in the box, it is when the soles of the shoe touch the table that the problems start

Spilling salt. Gotta chuck it over your shoulder and ask for forgiveness apparently...
Reading your own tea leaves. Mum used to read peoples' tea leaves and was quite accurate in her predictions. One of her friends, not knowing how "unfunny" it would be to Mum, switched cups and so Mum ended up reading her own. When she told her friend that one of her sons was going to be in an accident and something was going to happen to one of his legs her friend turned pale and admitted to what she had done. Mum freaked out and was not at all surprised when a few hours later the Police arrived to say my eldest brother had been knocked off his bicycle and was in hospital. He had multiple fractures of his right leg and was in hospital for six weeks. She never read tea leaves again.
Ouija Boards. Being a great believer in evil spirits (hence my missing out on the eclipse) she will not have anything to do with "opening a spiritual gate" because you never know what might come through. My sister ignored the warning and made a Ouija board and held a seance with her friends. That started the poltergeist troubles in the house we used to live in. Never thought that was evil but still, most of my friends only slept over once

She has many more that I only learn about as I stumble across them which usually involves some freaking out and dire warnings.
Never buy her pearls.
Never give her chrysanthemums.
etc etc....
Black Holes happen when God divides by zero.