Looking for word or succinct phrase for group incompetence

I'm looking for a non-vulgar word or short, succinct phrase to describe group behavior wherein all of the individuals are making the same stupid choice. The vulgar "clusterfuck" is close. Acting like "lemmings" has some of the connotations I'm looking for as well.

Example: The other day I drove to pick my son up at school. As usual, there was a traffic jam. On this day, it was made worse by the fact that a dozen people ignored the empty parking spots along the curb and instead waiting in line behind each other, causing a jam which spilled beyond the intersection, blocking traffic on other streets. It was an example of one person after another making the same stupid choice, rather than thinking for themselves. The situation was a real XXXX.

EDIT: As is often the case with English (maybe all natural languages?), the answers have provided multiple ways to say this, with multiple fine shadings of meaning. Thank you all. How do I fairly select only one answer as the answer, when several work well?

You pretty much have it with lemmings, and it's sad that the “vulgar” term says it best.

Polite versions of this might be, depending on context:

• there was a lot of groupthink going on
• the group displayed the worst kind of herd mentality
• the echo chamber was, alas, in full effect

and so on.

There are many other anecdotal descriptions, you might benefit from searching for quotations of e.g. Mark Twain (here is a good description of groupthink in other words), or our perennial favourite source of cynical quotes on the subject of intelligence, Albert Einstein (some examples from him and others on the rôle of education in exacerbating these phenomena).

See also this Guardian science blog discussing the negative effects of the “echo chamber”.

You may be able to use Monkey see, monkey do:

the act of mimicry, usually with limited knowledge and/or concern for the consequences.

Other phrases that occurred to me while reading your question are The blind leading the blind:

a situation where a person who knows nothing is getting advice and help from another person who knows almost nothing.

and The inmates are running the asylum:

The people least capable of running a group or organization are now in charge.  Said especially when the result is total chaos or calamity.

The blind leading the blind

is a very old expression of group incompetence. Its earliest known appearance is in Hindu scripture:

Fools dwelling in ignorance, yet imagining themselves wise and learned, go round and round in crooked ways, like the blind led by the blind.

• Katha Upanishad, part 2 verse 5, tr. Swami Paramananda

The Upanishad is being taken out of context to a certain extent, but this became a well enough saying to make it into the Gospels:

Let them alone: they be blind leaders of the blind. And if the blind lead the blind, both shall fall into the ditch.

• Matthew 15:14, KJV

And the saying's appearance in the Bible has led to its becoming a frequent subject of Western art.

The saying is so well known that it's now used for secular purposes, such as death march projects doomed to failure.

I'd call it a "domino effect":

"a series of similar or related events occurring as a direct and inevitable result of one initial event, a cumulative effect produced when one event sets off a chain of similar events.

But from another point of view, I might also call it "mass idiocy" or "mass ignorance"