1.Proof or evidence supporting your outlandish claims.
Origin is from the CARFAX.com commercials featuring a fox that is best known for saying, "show me the CARFAX," to unsuspecting car salesmen.
2. A list of people you've had sex with.
1. Person 1: I met Jay-Z last night!
Persion 2: Show me the carfax or it didn't happen.
2. Person 1: Person 1: So when are we gonna make it official and become a couple?
Person 2: You gotta show me the carfax before we get serious.