Vald's subsequent irritation at Havi's nonchalance. He spends so much time in Sincerity Mode that it's even funnier when he goes full Deadpan Snarker.
Vald: Oh, I get it. This was all my fault. Who cares about safety when there's magical bric-a-brac to hoard? Well, you can just go hoard yourself to death!
Halrein giving in to the Schmuck Bait presented by Vald's cuffs. He even gives the exact same reasoning as Havi did!
Halrein: Hey, Ruruka! How the hell was Halvir controlling this thing?
Havi calmly congratulating Vald on successfully killing him and Vald snapping and punching him is both this and a Tearjerker. Mars, Halrein, and Ruruka all reprimanding him for his insensitivity one after another is just straight-up hilarious.
Ruruka: Anyone who hurts Vald should be dead another time, you unsociable wizard.
The cover for one of the chapters where Vald is Disguised in Drag spoofs a fashion magazine, advertising "Princess Vald's" tips for cross-dressing successfully.
Halrein's vision in the "Havi Knows Everything" extra. While the others are suave and confident, Halrein is so awkward that even in his fantasies, he's a stuttering mess when Vald comes onto him. He tries to distract demon Vald by playing fetch.
Most of "Ruruka's Claim", really.
Ruruka briefly gaining Medium Awareness to shriek that Havi is no longer worthy of being a Seme because he lost his mind for an entire volume.
The Evil Sorcerer version of Havi in Ruruka's retelling is...just regular Havi, but with "evil" hovering next to his face.
The unstoppable force of Havi's jealousy meets the immovable object of Mars' utter obliviousness.
Mars: His Highness said that my pectoral muscles are magnificent and he touches them often.
Havi:(grabbing him by the collar) ...You. Why would there be a need for you to get naked in front of Vald?
Mars:(still cheerfully unconcerned) To give me a towel rub. It's a daily thing.
And Vald wandering up to this powderkeg of a conversation, totally unaware that he's the topic.
While stuck outside the dimension where Astador is holding Vald, Halrein warns that none of the party can use magic. Havi almost immediately forgets and attacks a monster with a fireball, resulting in both of them getting bound and suspended by a trap.
During the Enemy Without storyline near the end of the manga, Havi's utter failure to explain himself to the twin Valds without making one or both of them furious with him.
Havi: Listen to what I'm saying! Do you not believe me?