I here quote from an online chat conducted today by Washington Post columnist Gene Weingarten, a personal hero of mine:
Note: although GW simply says the first line of the poem need only be "gibberish," I have yet to see one of these begin with something other than "higgledy piggledy," and this in fact is another name for the form.A double dactyl is two quatrains containing a single rhyme, that being the final sound of each quatrain. With the exceptions of the final, rhyming lines, the entire poem must be in paired dactyls, each dactyl being one stressed syllable followed by two unstressed. The rhyming lines must have four and only four downbeats. Line breaks can be idiosyncratic.
Thus, you get two quatrains exactly like this:
DUM-dum-dum DUM-dum-dum
DUM-dum-dum DUM-dum-dum
DUM-dum-dum DUM-dum-dum
DUM-dum-dum DAH
In addition, the first line of the poem must be gibberish, and one line and only one line in the poem must be a dactylic six-syllable word. Generally the second line is a person's name, though variations are permitted.
Got it? Very demanding, waaay more so than a limerick. Very childish. Rather exciting, when you nail one.
The most famous double dactyl is probably this one, by John Hollander:
Higgledy piggledy
Benjamin Harrison
Twenty-third president
Was, and as such,
Served between Clevelands and,
Save for this trivial
Idiosyncrasy
Didn't do much.
My first attempt (which is admittedly pretty lame) is about the business trip I'm going on tomorrow:
I'm sure you lot can do better.Higgledy piggledy
Box-playing wage slave Ro3b
Goes to a meeting that
Frankly just sucks.
With resignation, he
Sits in a conference room
Digito-femurally
Playing the Bucks.