The joke is bad because the husband is supposed to bring seven gallons of milk. Since the egg condition is checked after he already got one.

Given the stereotypical difficulty of "product folks" and programmers agreeing on and building shared understanding of what to build, this joke seems clear and straightforward. It works because of course, the customer and the programmer failed to agree on something simple.

I'm pretty sure I've heard effectively the same core joke but better composed. Can't remember it though because at best it's middling funny.

Maybe it's just worse when written. The period at the end of the sentence makes it hard to see how it could be misunderstood.

To your point though, not sure if I'm aware of any programming language that would continue a statement with a following if block. Far more likely that it would fail due to lack of an element to apply the 6 to rather than having a pointer to the previous object, or he would try getting what ever the literal version of a 6 would be, or maybe some slang version.