After the Delorean brought them to ABC's studios in the middle of Kimmel's late night show, they got a rude awakening about what the future holds - i.e. Grindr and selfies. (To make matters worse, the Chicago Cubs were eliminated from the MLB playoffs last night.)
When Kimmel explained that most people would probably watch Doc and Marty's appearance the following day, while sitting on a toilet looking at their phones, Marty's reaction spoke for all of us: "That's gross."
Finally, Doc Brown decided to take matters into his own hands, and travel back through the space-time continuum to figure out exactly where mankind's evolution took a wrong turn.
Check out the Back to the Future reunion here: