Calling in sick

A guy works a new job on Thursday and Friday. On Monday he calls in and says, "I can't come in today. I'm sick."
He works the rest of the week, but the following Monday he calls in and says, "I can't come in today. I'm sick."
The boss asks the foreman about him, and the foreman says, "He's great. He does the work of two men. We need him."
So the boss calls the guy into his office, and says, "You seem to have a problem getting to work on Mondays. You're a good worker and I'd hate to fire you. What's the problem? Anything we can help you with? Drugs? Alcohol?"
The guy says, "No, I don't drink or do drugs. But my brother-in-law drinks every weekend, and then beats on my sister. So every Monday morning, I go over to make sure she's all right. She puts her head on my shoulder and cries, one thing leads to another, and the next thing you know, I'm fucking her."
The boss says, "You fuck your sister?"
The guy says, "Hey, I told you I was sick."