This gal works in a different department and has a different boss, she's also in her early 20s and not as experienced in the general work world. She was asked if she could cover an afternoon shift tomorrow but has plans so she offered to help in the morning. Her boss put her on the schedule for the afternoon shift (WTF?!). I coached her on how to call her boss and be polite, but absolutely firm that she can't work tomorrow afternoon. Remember: no is a complete sentence and you don't owe them an explanation as to why you can't work. Plans with roommates/family is a legitimate reason for not wanting to work.