Looks like a cheap joke to make, but it comes out genuine, as it was natural to say between officers who knows each others for a long time.

I know what you mean. I tend to follow the Joss Weedon technique of having most of the humour come from the characters saying amusing things in a way that makes sense, eg by being sarcastic or joking around with each other. It's all through Firefly, with lines like "yeah, well, I want to be Emperor of Mars and wear a shiny hat - just get it done."

Long time ago, I tried really hard, during my youth, to come up with funny characters but instead turned out to be the cringiest characters I ever created. It's been decades, and I still feel the shame and embarrassment ... and every time I think about this, I start drinking.

Oh god some of the stuff I wrote back then still makes me shudder. The biggest problem I had, other than inexperience, was that I was trying way too hard and forcing things to go my way. The way Paolini is still doing as we speak.