College football coaches are pretty funny.
Arkansas coach Bret Bielema recently joked about going to watch Michigan's open practice in Florida.
After seeing that, Michigan State head coach Mark Dantonio made a joke about going, as well as grabbing lunch. Everyone essentially thought that was the end of it.
The next day, Tennessee's Butch Jones asked to join. Still all in good fun, but Tennessee has enough unwanted attention.
It's probably not the best time to joke with all of the serious allegations surrouding the Vols' program. Evidently, Harbaugh felt the same, and sent out a not-so-subtle subtweet to the Tennessee coach.