Its a deal breaker sign that the person you are dating is not your "one". You will recognize a Canada Joke because:
1. You may immediately loose all sexual attraction to the person.
2. Lost your patience at anything this person continues to say because you subconsciously or consciously feel this person is too stupid or lame to carry on a decent conversation.
3. Get up and walk away for good without saying a word and without any remorse.
4. Any respect that was there is now gone for this person.
Originated from someone not getting a joke about canadians.
Me: He picked me up for the first time and I saw he had Ani DiFranco and Indigo Girls CDs in his car. I am so not going out with him again. What a pussy.
My Best Friend: Oh, that's so a Canada Joke.
Me: I know. Straight guys don't listen to Ani DiFranco and the Indigo Girls.