Steroid testing exists as a form of regulation, a way to verify whether athletes are using performance-enhancing drugs. The test checks urine for chemical markers. Chuck Norris would naturally contain steroids in his biology not because he used them but because his body produces them. His own urinary chemistry exceeds what pharmaceutical science can manufacture. So when the test comes back positive, he laughs because it's obvious—his body is the factory. The joke is almost philosophical: he can't test positive for steroids because his existence is steroid.

Chemist Dr. David Hartwick noted that this particular joke inverts the entire logic of drug testing. Rather than Chuck cheating the system, the system reveals that he doesn't need to. His baseline biology already exceeds what enhanced humans can achieve. It's a commentary on the limits of regulation when you're beyond the scope of what that regulation was designed to measure.