"Alright, I screwed up in the Dark Hour. My Persona went nuts when I summoned it. Shit happened. I'm not going back. Happy now?"
A short time after being confronted by Naoto, Roy casually tells Junpei:
"You do know the short one with the hat was a chick, right?"
"HULKSTER'S GONNA RUN WILD ON YOU!"
Captain Meathead Mc Protienboxer
Shinjiro's subsequent laughing fit. Made even funnier when his aunt and uncle don't seem too surprised by the event, simply commenting that it's been a few years since this happened.
Additionally, Akihiko is afraid of spiders. Not only is Roy's Persona Anasi a spider god, but he gets a pet tarantula in chapter 21. Needless to say, his reaction is priceless (and leads to another laughing fit from Shinjiro.)
"Seems his ability to act tough and intimidating just flies right out the window when he's laughing that hard."
The Crossdressing Pageant. Full Stop. Between Hamuko and Junpei - somehow - managing to win spots as Emcees - Dressed up as Jack Frost and Pyro Jack respectively - to Akihiko somehow being part of it, to the random student who wins it in a lovable nod to everyone's favorite blue bear
Really, the whole culture festival counts; the two junior classes pooling together to make a maid cafe - Shinjiro as the chef of all things - the Featherman stunt on day two, which also should count as an Awesome Moment,, the subsequent stealing of a prop from said stunt that involves Yakety Sax ... All that was missing was a visit from the Velvet Room to make the insanity complete.