The very first episode, when the then-unnamed Tora asks Ushio to free him from the spear. Ushio asks what Tora intends to do, and Tora replies that he'll eat him first and spread terror among humanity, heheheheHAHAHAHA~ooooooooowwwwwwww!!!! as Ushio starts stomping the spear deeper. And then he slips up and repeats the SAME THING when Ushio gives him a second hearing!. Tora really can be a moron at times...
In the same episode, his father tells a miffed Ushio from the gate to not eat his Chinese bun in the refrigerator. After encountering Tora in the basement, he goes to complain to his dad only to remember he was gone, so out of spite, he eats the bun.
Episode 3:
Tora laughing as Ushio gets beat up by an upperclassman in episode 3.
Ushio's father joking that Ushio must have the beast spear as he walks away from the breakfast table with it. He then has a hilarious Oh, Crap! face when he realizes the basement where Tora was imprisoned has been opened.
Tora mocking Ushio as he's being dragged into the painting to beg for his help. Ushio instead gets swallowed in. Tora initially claims "it is what it is", but then grows increasingly uneasy, and decides to rescue Ushio anyway.
Tora gets mad at how Ushio always seems to be getting Eaten Alive by other demons after saving him from the demon in the painting. But any time he tries to eat him, Ushio always beats him up instead.
Tora being a Fish out of Temporal Water in episode 4, and is completely unfamiliar with the city. He gets hit by a truck on the street, is unable to pass through windows in his invisible form, and finds the smell of perfume and cologne to be repugnant.
Episode 8:
Tora reacting like a child with free rein in a candy store when he sees airplanes for the first time.
Ushio applying the Reverse Psychology on Tora to trick him into taking the place of a landing gear for the plane.
The manga volumes sometimes have quizzes at the end of them. Often, they are three-answer questions where the two incorrect ones are patently silly. Special mention goes to the one where HakumennoMono is drawn in a super-deformed style.