I prefer to call her the first wife (apologies to Sir Clement Freud)

Also somehow saying she's my favourite wife was a problem, and yet "least favourite" was worse. Honestly!

The joke, loosely, is :

A wife asks her programmer husband” on your way home, can you swing by the store and buy one carton of milk, and if they have eggs, get six?”

It’s funnier and more relatable to programming if he comes home empty handed, crashes the car into the garage door, and says, with perfect alacrity, “six what?”