The line comes from a sketch in That Mitchell and Webb Look, the BBC comedy series starring David Mitchell and Robert Webb, in which two German soldiers chatting on duty slowly notice the skull badges on their caps and wonder what side they are on. Shared widely as a captioned image and short clip, it became shorthand online for a moment when someone finally recognises an obvious moral problem in their own position. It endures because the joke is not tied to one news story, so it can be reused whenever a group confronts an awkward truth about itself.