Chapter 366: Byakuran's attempt at searching for Mukuro involves blowing up a random car. Cue person running out of it while on fire.
Byakuran: Guess not, just an ordinary person~
Then there's the "Bowling" chapter, where Longchamp invites Tsuna and Gokudera to go on a three person blind date. Of course, Longchamp's idea of a "cute" girl has always been... unique. So the three girls he invited were absolutely hideous (one of them even being Reborn in an ugly drag). The whole chapter pretty much consists of Tsuna and all of his Bishōnen guardians / male friends coming by, being horrified by how ugly these women are, and then trying to run away from them as the women aggressively pursue them.
Technically, it is true that Reborn didn't see him.
Chapter 380: Everyone's reactions to Flan sleeping. Even Mukuro gets Blank White Eyes!
In an early chapter after Tsuna saves Gokudera's life Gokudera becomes devoted to Tsuna and says he'll place his life in his hands. Tsuna doesn't want this but Gokudera glares at him and Tsuna is shown thinking "Too...Too afraid to refuse...What kind of situation is this..."
Reborn's tendency to fall asleep whenever Tsuna is talking. In Chapter 391 after Tsuna makes his declaration that he won't let Reborn die Reborn responds by falling asleep complete with Snot Bubble.
Tsuna cannot tell who Adult!Reborn is. Chapter 402, and the Arcobaleno are doing their job to make sure it stays that way.
Hibari thinks the way to increase his flames to activate his ring is to get pissed off. Kusakabe and Genkishi immediately think together "That's wrong!!"
When protecting Yuni, Squalo and Hibari step up to protect her and Tsuna. Except Squalo is more in front and didn't notice Hibari. Hibari, instead of beating Squalo, pokes him with his tonfa and tells him to get out of his way. It's his vaguely polite expression and Squalo's reply to being poked that makes the scene funny: