Right after Snow Black reveals her true form, she asks Haru to take her flying. He is obviously flustered and nervous, and Snow Black is openly flirting with him. What makes this so funny is that we get a shot of Taku looking at them, obviously enjoying their little scene.
Shenanigans that occur when Black and Red kings stay for the night in Haruyuki's apartment. All of them, other than the few bits that were heart-warming instead, beginning from Snow Black's attempted departure.
When Snow Black tells Haru that she'd give her anything he wants, the first thing that comes to Haru's mind is friggin' food.
The second ending. Kuroyukihime vs her net avatar.
When Silver Crow confirms his metal armor has cold resistance, Scarlet Rain decides to test this for herself by pouncing on his back and assaulting him with snowballs from the Snow and Ice stage. And if that wasn't funny enough, her gleeful facial expressions just sell the scene.
In episode 9, Haruyuki and Kuroyukihime enter his apartment to find Yuniko playing his (rather gory) video games. The look on poor Haru's face is priceless. The scene is made even funnier in the English dub, in which the first thing that greets Haru when he opens the door is Yuniko yelling, "DIE, SUCKERS! BURN IN HELL!"
In episode 24 Haru asks Kuroyukihime to "be with him forever". This causes Kuroyukihime to absolutelyfreakout. Haru doesn't follow until he figures out how it came across, and immediately gets flustered.