The actor was stopped by officers in Los Angeles and feared the patrolman who pulled his vehicle over would use the opportunity to punish him for his breakthrough part on teen drama, The O.C.
But McKenzie breathed a sigh of relief when he was let off with just a warning - thanks to his role as an LAPD patrol officer in Southland.
The star tells U.S. talk show host Jimmy Kimmel, "We're driving back on the 10 Freeway and I'm having a little bit of a fight with my girlfriend, and I'm not really paying attention to the road. Sure enough, a cop pulls up behind me.
"Then I hear, 'Are you who I think you are?' Immediately two thoughts occur to me: This could be either really good, or really bad. Really good if it's Southland, right? If he recognises me from Southland because (it's about) law enforcement, he'll probably love this. If it's The O.C., he's gonna give me a ticket, he might put me in jail - who knows?
"So again (he asks), 'Are you who I think you are?' I say, 'Yes sir. Southland?' He goes, 'Alright... Watch your speed,' and gives me back my licence!"