Hitler's last supper is a scene in Downfall that is used quite often in parodies.
Hitler, Constanze Manziarly, Traudl Junge and Gerda Christian are all having a meal in the Planning Room. At this point the women know this would be Hitler's last supper. Everyone is eating silently. Traudl is seen glancing frequently at Hitler's left hand, which is shaking badly.
After finishing his meal, Hitler thanks Constanze, who prepared the food. He then wipes his mouth, and walks out. Those who remain don't continue their meal, except Traudl who takes one bite, but it's apparent that they have lost their appetite.
In the parodies
Parodies using this scene depict some dining table shenanigans, including Hitler refusing to eat, or taking a bite and then taking it out again.
The part where Traudl glances at Hitler's shaking hand has been parodied in a sensual manner.
Some Bunker Jokes make fun of Hitler's Alzheimer's, in a similar manner to Michael J. Fox jokes.