The optional death scene in the second game, complete with old-school Sierra-style Restore/Restart/Quit screen.
In the prologue for Chaos on Deponia, Rufus sees a button with a dusty display that can change to one of three options that could save him when blown upon. After pressing it, however, nothing seems to happen, causing him to blow off the rest of the dust for answers. It turns out to be an "Eject Goal" button.
The pre-Act 3 ballad from Chaos on Deponia ends with a moment that calls to mind the famed lumberjack song from Monty Python's Flying Circus:
The showdown was imminent
And if not, I apprehend
The chorus guys will have to work overtime
(Huzzah, we'll work... overtime? Wait, what?)
Near the end of Goodbye Deponia, Rufus has to make an inspirational speech to the Organon army while pretending to be Argus, but accidentally speaks about "that ass" over the microphone, referring to Argus. He makes it work, splendidly.