I'm sick...

This guy is looking for some help at his manufacturing plant so he puts an ad in the paper.
This guy shows up so he puts him to work and this guy is a fantastic worker, never had anyone better. Monday rolls along and the guy gets a phone call from his new employee. "Can't come in today, I'm sick."
So the guy figures what the hell. Tuesday to Friday the new guy's back and again a fantastic job, couldn't be better.
Monday rolls along and the guy gets a phone call from his new employee again. "Can't come in today, I'm sick."
The boss sighs but he's never had such a good employee so what the hell. Tuesday to Friday the new guy's just great but again on Monday morning the boss gets the phone call. "Can't come in today, I'm sick."
Tuesday the boss sits the new guy down. "So what's up with this crap you keep pulling on Mondays? I mean you're the best employee I've ever had and I'd hate to let you go but what's up with this?"
"Well every Monday on my way to work I stop by my sister's place just to see how she's doing and well one thing leads to another and we end up spending the rest of the day screwing our brains out."
"Oh CHRIST that's disgusting!!!!!!"
"HEY, I told you I was sick..."