The story starts with Konohamaru confronting Naruto after some untold stories of various missions with an ultimatum that Naruto couldn't refuse. Konohamaru seemed particularly confident in his ability to take on his boss now. Naruto, of course, wasn't going to take him 100% seriously because he had beaten things far worse than Konohamaru so why not.
He let Konohamaru call the shots when it came to the deal they had struck. If he lost in their fight then Konohamaru would be the "Boss" now. Konohamaru shook his hand, they went out back, and Naruto got a huge thrashing. It seemed impossible but the rule of thumb is that truth is more stranger than fiction. Some kids just develop faster. Konohamaru made Chunin for his accomplishment. Naruto had just been a Genin and now he's even less than that since the new boss has decided that Naruto needs to go back to the academy. Considering who he lost to, there's no doubt they'll take him back. Paperwork has already been finalized.
With a spring in his step and a wish of good luck, he gave Naruto a painful hanging wedgie and left him hanging on the door of one of the Academy classrooms in his destroyed outfit. The Pixar's Cars briefs would probably be a dead give away that he was probably more suited for daycare but Konohamaru wanted to be generous. When Naruto woke up from his knocked silly state, he'd be particularly uncomfortable and positively unwilling to do this but he won't have much of a choice. His new boss demanded it. So much for being Hokage.
