Favorite Young Ones Bit #1:
In the middle of a sketch, the action freezes and the camera zooms in on a box on the closet shelf in the background. The box is actually a puppet with an articulated lid.
Box: "Don't look at me! I'm irrelevant!"
The camera zooms back out to its original position and the action resumes.
Favorite Young Ones Bit #2:
Mike comes downstairs angrily, while Vyvyan reads on the couch.
Mike: "What's the fish doing in my bed?"
Vyv, not even looking up: "What fish, Mike?"
Mike pauses, then goes back upstairs: "Right. Right."
A little later, Mike returns holding a tuna fish (or possibly a sea bass, I'm no ichthyologist or anything...) nearly as big as he is.
Mike: "Right. Now, what's this fish doing in my bed?"
Vyv, again not even looking up from his task (I believe he was about to do violence to Neal): "That fish isn't in your bed, Mike."
Mike blinks at Vyv's flawless logic, then returns upstairs, fish in hand: "Right! Right!"
Even later, Mike drags Vyv, Rik, and Neal into his room bodily, showing them the large fish tucked in beneath the covers with care.
Mike, with an air if triumph: "Right! Now, what's this fish doing in my bed?"
Vyv, pointing out the bleedin' obvious: "Well, you just put it there now, didn't you Mike?"