Flapjack barges into Doctor Barber's place, while he is treating a patient in a darkly-lit room. Doctor Barber turns around and is all covered in red stuff, looking menacing. He then takes a step to the side, kindly asking if Flapjack wants a strawberry-jam sandwich; and there is a plate of strawberry jam sandwiches lying on the patient's stomach.
Most of the Nightmare Fuel moments also qualify as this, which means there are LOTS of these:
In "Mechanical Genie Island", K'nuckles is fed up with being a mechanical genie's slave, freaks out and quits. It has to be seen to be believed.
Flapjack and Knuckles hilariously abusing the Magic Mermaid Wishes for ridiculously petty wishes, such as Flapjacks wish for "x-ray vision, freakishly tall legs and the ability to spit anchors", and Knuckles wasting wishes on moving a suitcase around.
Also borders on Nightmare Fuel, but the Sky Maid's parting speech to Flapjack.
Sky Maid: And remember Flapjack, keep wishing, and all your dreams will come true!