He's not giving you the head-slap, he's giving it to himself. It's sort of an inside joke. He doesn't have a metal lathe, but wants one real bad and is working on getting one. It's sort of a fundamental metal shop tool and he doesn't have one while he does have a CNC machine, which is a pretty advanced tool.
To be fair, it's often tough to decide what to invest in first when it comes to complex tools. I know from building more than one wood shop, one tool is often not as useful as it could be without another. For instance, do you buy a drill press or a table saw first? Or, do you dedicate the space to a big, fluffy bandsaw? And if so, where do you put the surface mill? They're fun problems, though.