No citations here but, from past experiences and my personal opinion:
It partially depends upon the social context:
If you laugh at your own jokes when you're chatting around with people and they arn't laughing as if it were a "group syncronized" event then it appears (and I feel) that most of the time not only does it come across as "try-hard" but actually is "try-hard."
I believe that emotions are contagious, and I believe that people know this on an intuitive level. Thus, they're trying to make themselves seem funny by laughing at something that wasn't by hopefully convincing you/the group that it's funny as well as spread the emotion.
There's a subtle difference though. There are rare occasions when that wasn't the intention and someone just genuinely thought what they said or whatever they thought was funny was funny. In these cases you'd have to distinguish between "narcissistic and genuinely confident/carefree." Is there a difference? If so what is it? To me, narcissism implies pathology. I'd say there's a correlation between the two, but not a direct y=mx one.
When trying to build rapport with someone (like say your boss, or someone you like you just met) you'll notice yourself laughing much more than usual. Laughter builds rapport (you're sharing an emotion with someone)...so it's as if we are subconsciously trying to build rapport with these people moreso than "---may be---" natural. Sometimes they can even sense that and it turns them away/off. I emphasize the word "may be," because both parties could be having a similarly good time and both equally interested in talking to the other. In other words, they are "synchronized."
Now, If you're alone and you're laughing at yourself that is truly genuine. You're not trying to make other people laugh because no-one is around. Is that narcissistic? Or is it carefree about the moment/confident? That kind of boils down to a game of semantics. To me narcissism implies pathology as I said up there, and I don't think the relationship is y=mx, but one of many independent variables pointing towards narcissism.
I am a little bit confused as to how you went straight to "narcissistic features." The question itself seems to assume that John Hodgman himself is narcissistic or has narcissistic like features.
From what you've quoted, he's not saying that he laughs at all of his jokes as he's trying to come up with bits for his comedy act. If he did that, then yes, in my opinion, that would be weird and probably narcissistic if not completely insane.
However, he's saying that the way he decides on whether or not he wants to use, in the future, that particular thought or bit that made he himself laugh while (assumedly) he is alone (which you have to admit that's not necessarily an easy thing to do...in fact I think you'd agree with me that it's quite hard), then it passes his test and is funny enough for him to use on an audience.
There have been moments where you have been alone and laughed at yourself or laughed at something you saw, or maybe a thought you came up with, right? Everyone has.
You also have to take into consideration different styles of humor. If the comedian thinks his jokes are funny (I mean, if he hand picked them in that specific style then he probably would...who knows he could have gone through HUNDREDS of jokes he thought were stupid until he found one that made him laugh) but someone else doesn't think his jokes are funny I could see how that could be potentially misinterpreted as narcissism; but, once again, you have to account for the different styles and quirks of humor each and every person thinks is or is not funny too.
Just because a comedian would laugh at a joke that they had hand selected as having the quality of making themselves laugh and someone in the audience has different tastes, that doesn't mean that the comedian has narcissistic features.