I'm curious if he meant it as a joke, expecting Tucker to laugh, or if he intended to insult him. It actually could have been a translation thing because the insult was a bit subtle. The translation was like "maybe it's best you didn't join, because the cia is a serious organization." Could have meant something like "fuck the cia, your better off not being in it." Or maybe he's implying that Tucker has cooperated with the cia.