Oil on just 1 spark plug?

Was giving my 2nd Gen V6 a tune up, and 1 of the 6 spark plugs had oil on it. Pic below. I'm not super technically savvy, any idea why only 1 (the plug closest to the driver, drivers side "rear" plug) has oil and the others dont?

 

The plug is not in my hands, so I can't say for sure, but it looks like the oil is likely coming from outside and not the result of rings/valves/guides/seals leaking internally.
You may have a leaking valve cover gasket. I would eyeball that area more closely.
What yr. is your truck? The head gasket alarmists will chime in if you say 2005 or 2006.

 

This was my initial thought as well. The business side of the plug appears relatively clean. I suspect your oil problem is above the plug, most likely a valve cover.

 

It’s a 2006...and you’re correct, the threads are clean. The oil was on the top part of the plug.