I'm not going to pick up my coworkers shift
Oh really? Why don't you want to pick up their shift?
I hate working on weekends, I don't want to work a Sunday.
You should try to help out your coworker once in a while. They need you sometimes and it's only fair if they help you.
I don't want to, I'm lazy and hate working. What do you think of that?
What if you needed a shift covered, wouldn't you be mad if no one helped out? You should put yourself in your coworker's shoes.