I'm sure I mentioned this here before, but anyway…

The CIA trains a special agent for a mission to Russia. The program ensures he's able to perfectly blend in with the local culture. The agent gets dropped off in the middle of Siberia, goes into the local pub and orders vodka.
All the while, he's been feeling like everyone's staring at him, and finally some old man tells him: "You're not a Rus."
The agent says with perfect accent: "How am I not a Rus? Look, I can drink like one!" – drinks a bottle of vodka and orders another.
But the old man insists, "You're not a Rus."
The agent tries again: "I can dance Russian dances too!", and dances perfect kazachok for several minutes. But the old man says again: "You're not a Rus."
The agent tries several more times, but the old man can't be convinced, and he doesn't have much luck anywhere else either. He returns home to report about the failure of his mission. His boss is pissed off and shouts: "I knew you blacks will fuck up everything!"

detecting Russians has been harder since they stopped being commies