A mystery illness that usually occurs on a Friday or a Monday, typically during the spring, summer, and early fall on fair, sunny days. Symptoms include distraction and an urge to call in sick. The only known treatment is to increase use of recreational facilities, such as golf courses, city parks, or beaches.
"This is the second Friday in a row that Bob's called out sick."
"Yeah, and it's 75 and cloudless today. Pretty sure he's got a nasty case of the 18 hole flu."