Conan served as president of the legendary Harvard Lampoon during his time in Cambridge. He earned a reputation as a prankster. At least two pranks attributed to him have become the stuff of legend — and a third came back to haunt all parties involved.
The first one, confirmed by the parties involved, occurred when Burt Ward came to lecture about his time playing Robin on the classic '60s show "Batman." Ward boasted in flyers that his costume was worth half a million dollars, so O'Brien became determined to take him down a peg. As such, O'Brien and a friend showed up in security guard outfits to the speech, claiming to Ward that the dean sent them to protect the costume. During a Q&A, another friend dressed up as the Penguin stood up and asked "When is a costume not a costume? When it's stolen." Someone hit the lights, at which point they grabbed the costume and ran off — then spent the day calling Ward and taunting him like a Batman villain.
The second was reported by Harvard Magazine, who noted that O'Brien declined to comment "on advice of counsel" about this legend. As the story goes, O'Brien (allegedly) and a group of his friends somehow got their hands on a jackhammer and other construction gear. They dressed up in hard hats and started tearing up the pavement. He called the Boston police to report that college students dressed as construction workers were ripping up the street. He then called the Massachusetts state police, claiming to be construction workers being harassed by college students dressed as local cops. As such, the Massachusetts police showed up to arrest the Boston police who showed up to arrest the college students.
The third, and most prescient, was the time that Jeff Zucker called the cops on Conan. This was back in the '80s, when O'Brien was in charge of the Lampoon and Zucker was the president of the Harvard Crimson. The two papers have a longstanding rivalry, and O'Brien orchestrated stealing an entire print run of the Crimson before it could be distributed as part of a prank war. This whole exchange was unearthed by Deadline in the waning days of the 2010 "Tonight Show" conflict, during which Zucker had once again caused problems for Conan.