A guy works at a new job on Thursday and Friday. On Monday he calls in and 
says, "I can't come in today. I'm sick." 

 He worked 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 screwing her." 

 The boss says, "You screw your sister?" 

 The guy says, "Hey, I told you I was sick."