Leslie Odom Jr. is edging painfully close to the end of his time in Hamilton, and — life-changing, hugely fulfilling artistic experience aside — the senioritis is getting to him. For the past couple of months, Odom Jr. has kept a vlog, “Aaron Burr, Sir,” and this week, joined backstage by theatergoers Josh Gad and Dan Stevens and co-star Rory O’Malley, things got silly. You see, Odom Jr., Gad, and O’Malley all attended Carnegie Mellon at the same time (Gad and O’Malley were even roommates), and for a brief bit, they had another impressive college buddy: Josh Groban. Groban’s joining the Great White Way in Natasha, Pierre and the Great Comet of 1812 soon, so the trio (plus a game Stevens) decided to give their former classmate a big Broadway welcome with a good ol’ prank phone call. They razzed on Groban good, wailing classic Groban tunes like “You Raise Me Up,” and later, Josh and Josh had a chat. Of course, it took a bunch of tight-knit theater nerds to make Matthew Crawley feel like an outsider again.