Jon Gruden dropped in and surprised an online Univ. of Tennessee stats class this week ... and it was hilarious -- mostly because the guy absolutely sucks at using Zoom!!
The Raiders head coach -- who has an affinity for the Vols (remember #Grumors?) -- surprised a group of students Thursday that included star RB Ty Chandler ... but he didn't exactly pull off the drop-in without a hitch.
As soon as JG busted in the class ... his camera wasn't working and students couldn't see him. Later, the 56-year-old had a hell of a time trying to sign out.