Self-inflicted illnesses

You wouldn't believe how many crew members at McDonald's suddenly call in on Saturday mornings because they are "sick". Ok, I might have been born at night but it wasn't LAST night. Even I can tell that the person's illness was entirely self-inflicted. What does that mean?

It means that they spent a great deal of the night before drinking and getting drunk. Then they're sick the next morning and can't seem to function properly. Maybe we should stock the first aid kit with hangover cures and remove their excuses for not showing up at work and leaving us shorthanded for the shift.