I'm not going to cover a shift for a sick co-worker
Why wouldn't you cover a shift?
My boss told me I need to cover the shift or he would give me a hard time.
You should help out your coworkers especially if they are sick. It is important for them to stay home and not spread disease to others.
Ugh, no I don't want to.
At the end of the day it's your choice, but I'm sure your coworker would really appreciate it since they'd want to stay home and rest.