If you only have canned whole tomatoes and need chopped tomatoes, use a pair of kitchen scissors to cut them up while still in the can. It is much less messy that doing it with a knife on a cutting board.
I used to do it that way too, but I have had tomato juice squirt all over the place. I tend to be messy, so I started using the scissors.
Funny until time to clean it up. Funnier yet, once a fiend at dinner replaced the ketchup cap but didn’t screw it on. I always shake a ketchup bottle before I use is. You know “the rest of the story.” (The late Paul Harvey)