This one is very childish. One example: "No Scotsman puts sugar on his porridge." Joe said. "Angus is a Scotsman, and he puts sugar on his porridge." Interjected Tim. Then Joe smiles and replies, "Ah, but no 'true' Scotsman puts sugar on his porridge."

Another classical example:
Atheist: "No scientist believes that God created in six days."
Christian: "I'm a scientist and I believe that."
Atheist: "But no 'true' scientist believes that."

One more:
Atheist: "No peer-reviewed science journal would accept creation."
Christian: "The Answer Research Journal accepts creation."
Atheist: "Yeah, but no 'real' scientific peer reviewed journal accepts creation."