Jack Hoffa is not a real person (that I know of), but, a slang name signifying "Jack Offer". Although it might remind you of Jimmy Hoffa, the legendary union leader who came up missing and has been mostly presumed to have been killed by the mafia.
PETER: I accidentally walked in on my roomate dude ... Jack Hoffa!
BOBBY: No way!
PETER: Oh my dog! Unfortunately, it is TRUE!
BOBBY: Oh man, how embarassing. What did you do?
PETER: I said, "Hey man, what's ... oh sorry ..." and then I just shut the door, and drove to the mall, and came home real late. And the next morning, we both just acted like it never happened. I've never brought it up, and neither has he.