Any time Calypso received a wish too warped in itself. Hammerhead in the first game wished for TIRES.
The "Lost Ending" version of Thumper's ending in the first game. Thumper's driver wants to save his girlfriend from a rival ganglord. Calypso has the ganglord tied to a chair and the girl, unharmed, standing by. He also has a gun in hand, and offers it to the driver... The driver refuses to shoot, walking away with his girlfriend. Calypso blinks, and then mutters, "That was anticlimatic," before putting the gun to the ganglord's head himself.
Adding to the hilarity is the ganglord's deadpan, almost bored-sounding response of "oh, my god" just as he's about to be shot.
Axel's ending in Head-On; a mad scientist bound him to his old car, and forced him to enter Twisted Metal as payback for replacing the arms and legs Axel tore off in his ending in II. Axel was supposed to give his wish to the scientist, but after seeing all of the death and destruction caused by the contest, decides against it. Realizing what's happening, Dr. Zeemu shocks Axel, causing his wish to come out as, "I wish for Peace-AHHH!"
No-Face's last line in the game after he gets his prize.
"Ya know, that was the first time I ever knocked someone out with one punch."
Minion's ending in 2. Especially Calypso's childish and frightened begging as Minion throws him into Hell.
Shadow's ending in Head-On. One of the few times Calypso doesn't even try to screw over the winner for once (though he did try to suggest Mortimer to wish for killing the kids who woke him up), he actually complies with Mortimer's request and sends him back to sleep in his grave. How, you ask? By reading him a bedtime story about his victory while he's lying in his coffin with a teddy bear, complete withkindergarten-style crayon drawings!