I take my conlanging seriously, even if the tone I use in talking about it is light-hearted. I may frequently experiment with different methods of language creation, but no matter what particular process I am using, I have goals for that I am working to achieve, and often it really is work. Conlanging takes too much time, effort, and brainpower for me to not take my own projects seriously, even if I write about them in a less-than-completely-serious tone.
Nonetheless, I do find ways to integrate some humor and personally meaningful references into my languages in subtle (or not-so-subtle) ways, hidden in places that it can delight me without standing out as a joke to anyone else. For example, I recently created a word for "dragonfly" in Nevashi, ti'izirí. The word literally means "catfly" being made up of the words for "cat" (ti'i) and a general term for "flying insect" (zirí). It contains both a meaningful personal reference from my life and an inside joke: ti'i was the way my youngest daughter pronounced "kitty" when she was first learning to talk, and now that she is 7-years-old, we have long discussions in which I claim to not be able to tell the difference between a cat and a dragon because they look identical to me, and she patiently explains to me again the ways in which they are different, hence the substitution of "cat" for "dragon". The official explanation (if anyone asks) will be that the long tail and big eyes of a dragonfly remind Nevashi speakers of a cat, but now you know the truth.
Then there is the less subtle case of dali in ea-luna, meaning "to paint" in the artistic sense, not in the "covering something in a coat of paint" sense. This is a reference to Salvador Dalí, one of my favorite painters, but in this instance, the word pre-existed the reference in a raw list of potential 1- and 2-syllable words. When I came to that particular combination of syllables in the list, I knew what it had to mean. It's that sort of little thing that makes me smile when I come across it again in my notes, even if I never have a need to use that word in public where other people might see and get the reference.
An inside joke that you have with yourself about your personal life encoded into a conlang (as with ti'izirí) is just about as inside as an inside joke can get, but who cares if nobody else gets your little joke? I find the most subtle ones are the ones that make me happiest, especially when they are in a more serious project.