A very long time ago, a tribe of early human was trembling on the verge of an intellectual breakthrough. These people had, for generations, been using simple sounds to signify certain concepts: for instance, "cold," "hot," "danger," "follow," "jerkface."* However, some young and clever members of the tribe had lately been discovering that they could make more sounds, which would then mean more things. A rudimentary grammar was beginning to form.
One day, as the sun rose over the veldt, one of these intelligent young people turned to the other and made the very same joke that Marvin makes today. In that instant, language was born.
I think perhaps what I'm trying to say is that today's Marvin does not tell a new joke. Technically, of course, it doesn't really tell a joke at all...but the attempted joke in this comic is so creaky that poking it with a stick would probably cause it to collapse into a pile of dust. Throughout the twentieth and twenty-first centuries, other cartoonists have created comics featuring this exact same joke. I really hate this joke. I have read it so many times in so many different (albeit ominously similar) forms that I am even now resisting an urge to beat it with a baseball bat until it stops moving.
It works well in Middle English because it was old even in 1350. If Tom Armstrong had been writing then, he probably would have attributed the joke to Isidore of Seville.** Geoffrey Chaucer likely rolled his eyes when he heard this joke. What I think I'm driving at is that it's old. It's old, Tom Armstrong. You are telling an old joke. You are always telling old jokes. Either stop it now or get in your handy time machine and go back to school early humans in the art of non-humour. You are, after all, the past master of that.
P.S.: "Marvin knoueth a flie in milk" is a medieval way of saying, "Marvin can see the obvious." Yes...yes, he can.
*There has been a word for "jerkface" since humans became capable of rational thought, plus possibly for some time before that.
**Cardinal rule for medieval writers: if in doubt, attribute it to Isidore of Seville.