https://groups.google.com/g/rec.photo.equipment.medium-format/c/Cwpq_aGDLnU?pli=1

Scroll all the way down to the post of Jun 14, 1997, 8:00:00 AM by Danny Gonzalez.  He quotes a post from the rec.photo.equipment.medium-format (Yahoo?) newsgroup of 9 months previously.  It has the quote you are looking for.

No, and I thought I had heard every joke about the 6x7. It sounds like
something Mike Johnston would come up with.

bill

On Thu., Feb. 25, 2021, 2:19 p.m. Ralf R Radermacher, fotoralf@gmx.de
wrote:

Someone wh worked for Delphi.

If so, some basic truths must be revealed.

First of all, you should know that the Pentax 67 was never
designed as an actual camera for shooting: it was a display
device to be hung out in front of camera stores, over the
sidewalk. The first photographer to actually cock and fire one
noticed that, though his hair had turned white from the
shockwave, his sinuses had instantly cleared. After the hernia
operation, he used his Pentax 67 constantly, especially at the
onset of a cold or flu.

Body-builders were also attracted to the Pentax 67. They didn't
care that portraits from these cameras always showed people who
looked wide-eyed and startled, as if they had been recently
frightened by a loud noise. These cameras were great for pumped
and ripped upper-bodies.

Press photogs cherished their P67's when covering hurricanes and
tidal waves: they'd shoot with their Nikons and lash themselves
to their Pentaxes! But I digress.

You asked about the kerplunk, er kachunk, eh? Well, long, long
ago, before "red eye" was a problem for flash photographers,
Pentax 67 shooters were coping with the problem of "red EAR":

Color portraits and candids shot with Pentax 67's showed subjects
with crimson ears from the repeated auditory abuse they suffered
each time the camera was fired.

By the way, rumor has it that Pentax is currently
researching a solution based on existing red-eye reduction
technology (a series of quick pre-flashes before the real
flash fires).

The new Pentax 67 may include new red-EAR reduction
technology, which slams a heavy screen door a few times
before the actual exposure, to numb the subjects' ears
immediately before the shutter actually trips.

The other problem directly attributable to the impact of the
Pentax 67 mirror-return, is a type of focus blur. After the
shutter-release is tripped, the sonic boom begins advancing from
the camera toward the subject at mach 1. The wave-front reaches
the subjects just as the shutter opens, and the subjects are
knocked backwards, sometimes by mere millimeters, sometimes by a
zipcode or two.

Consequently, Pentax 67 lenses have an extra focusing mark
on their focusing-rings, similar to the "infra-red focus"
mark on other lenses.

This SSR pre-focus mark ("Sonic Subject Relocation")
predicts the focus for the spot where the subjects will
come to rest after the blast. It is to be used only when
shooting the P67 in small unmuffled rooms.
</quote>

It could also part crowds.

Decades ago, I was in DC on a lovely morning and decided I wanted to get a
different angle on the Lincoln Memorial.  I took my film 35 mm SLR out of
my camera bag and started wandering around, just looking through the
viewfinder from various vantage points.  I never got off a shot.  Every
time I thought I might have something, someone in the throng pushed or
jostled me, or just stepped right in front of me.

I went back to the camera bag to put away my SLR.  On a whim, instead of
closing the bag, I pulled out my Pentax 6X7, with the wooden grip and the
huge lens.  Heavy as it was, I trudged back towards the memorial.
Miraculously, the mob in front of the memorial parted, to let me through.
People actually moved aside and watched in awe as I struggled to get that
demon up to my eye and frame an image.  I swear I heard an audible "AHH"
when I pressed the shutter release and that resounding "CLUNK" bounced off
the Marble walls.  'Twas a strange but rewarding experience.

Dan Matyola
https://tinyurl.com/DJM-Pentax-Gallery
https://tinyurl.com/DJM-Pentax-Gallery

On Thu, Feb 25, 2021 at 3:19 PM Ralf R Radermacher fotoralf@gmx.de wrote:

Am 25.02.21 um 22:14 schrieb mike wilson:

Exactly. Thanks a lot. A friend has bought a used 6x7, although I think
it is a fake. It has paint on all corners. ;-)

Ralf

--
Ralf R. Radermacher  -  Köln/Cologne, Germany
Blog  : http://the-real-fotoralf.blogspot.com
Audio : http://aporee.org/maps/projects/fotoralf
Web  : http://www.fotoralf.de

On Thu, Feb 25, 2021 at 5:22 PM Ralf R Radermacher fotoralf@gmx.de wrote:

My buddy calls my 6x7 the KA LUNK camera

Dave

--
Documenting Life in Rural Ontario.
www.caughtinmotion.com
http://brooksinthecountry.blogspot.com/
York Region, Ontario, Canada

On Fri., Feb. 26, 2021, 7:16 a.m. David J Brooks, pentkon52@gmail.com
wrote:

I called mine Bruce. It avoided any confusion.

bill.

"The theory was that the mirror slap was so loud it would push a person
backwards and result in unsharp photos".

Reminds me of a chap here who claimed the spotlights on his bakkie were
so powerful (bright) he couldn't get into his garage until he turned
then off!

Alan C

On 25-Feb-21 10:19 PM, Ralf R Radermacher wrote:

Trying again.

-------- Forwarded Message --------
Subject: Re: Looking for funny text about 67 mirror slap
Date: Fri, 26 Feb 2021 18:46:51 +0200
From: Alan C cole@lantic.net
To: pdml@pdml.net

"The theory was that the mirror slap was so loud it would push a person
backwards and result in unsharp photos".

Reminds me of a chap here who claimed the spotlights on his bakkie were
so powerful (bright) he couldn't get into his garage until he turned
then off!

Alan C

On 25-Feb-21 10:19 PM, Ralf R Radermacher wrote: