Rick rolled by nazis during WW2. Used as propaganda by the nazis to persuade people to follow their ideas.
Often simplified as simply being footage of nazis with Never Gonna Give You Up by Rick Astley as the backing track.
Examples of reichrolls can be seen in various Downfall parodies.
Dude: Fuck! Reich Roll'd again!
Hitler: Scheisse! Das war ein Reichroll nochmal!
Historian: The Nazis used the famous reichroll very effectively to gain the support of the german people