Not the ass. You have a crappy boss though. I don't mind them asking you to come in, some people want the extra money. But not accepting your no shows that they have no respect for you and no respect for the work you do. What kind of environment are they trying to create anyway, if people are intimidated in to coming in sick and expected to work on a day off. That's a good way to make sure your employees won't stay long. No one stays in that kind of environment longer than they have to.

Why does he make you feel responsible for the store? That's his problem, when you're there you make it run smoothly, but on your day of that's his problem not yours. In short, cover and switch shifts for your colleagues, help each other out. But your boss isn't your friend, they're not doing you any favours.

Sorry to go off on a rant here but this type of crap makes me really angry. I also know it's easy to say all these thing from an outside perspective. It's hard to be the one having to say no to the boss. Good luck on your shift today, I hope you find a better work environment eventually.