I would love to hear how the ground of the mic (the negative DC supply) could cause this, and also how the ground of a phantom mic is different than the ground of a dynamic mic are different.

What does the 48V phantom power have to do with it? By the very nature of a phanto0m supply, the current is limited by the resistors in the mic preamp, and the + does not appear on the casing. If it did, then the 48V would be shorted to ground.

Dynamic mic automatically reject the DC voltage of a phantom supply, which is equal to both pins 2 and 3 of the XLR when phantom voltage is applied

That is NOT the issue, but often blamed by people who have no idea how phantom power works.

Lol phantom power is barely enough to power a small LED. This is an ungrounded guitar amp most likely.

Andrew Uher 48v can power 9 leds!

Ivan Beaver what if that cable is cut and no longer grounded, what if that pin is GONE. Explain Mr. I only work with grade A equipment paid for by the company I work for and have no idea how a current could mistakenly pass thru a metal object.. SYBAU

Rich YR If the ground wire is broken (or pin missing) a Dynamic mic will operate just fine, because the signal flows between pins 2 and 3.

A phantom powered mic will NOT work, because it has no negative of the power supply which is needed for operation.

But with either mic, if the wire is broken anywhere, then the case is not connected to anything, and therefore would not provide a path for anything, and could not cause what is being demonstrated in the original post.

“If the ground wire is broken (or pin missing) a Dynamic mic will operate just fine”
True
“A phantom powered mic will NOT work, because it has no negative of the power supply which is needed for operation.”
True
“But with either mic, if the wire is broken anywhere, then the case is not connected to anything, and therefore would not provide a path for anything, and could not cause what is being demonstrated in the original post.”
With a phantom powered mic with ground connection cut, there will be 48V phantom power through mic electronics on the mic metal body.
With dynamic mic, typically the signal wires inside mic are floating not connected to mic body, so no 48V phantom will not get to mic body. But it is possible that some mics can be built with built in center tapped transformer with center tap connected to ground pin – this would let the 48V phantom power to mic case.

Phantom voltage is supplied to the microphone via 6.81kΩ resistors on pins 2 and 3 (the return is pin 1, the cable shield). Pin 1 is typically connected to microphone metal body. If the pin 1 looses ground connection through the cable with classic dynamic microphone nothing happens (potentially mic picks more humming noise). If the microphone is phantom powered or has a built in audio transformer with output center point grounded to pin 1, the 48V phantom power cab get to microphone body.

https://www.facebook.com/share/v/1Cih5hq7vn/

https://www.sounddevices.com/the-danger-of-applying-phantom-power-to-unbalanced-outputs/

However, plug a line out into a P48 mic in – damage will be NONE and you will be instantly (and loudly!) reminded of how incompetent you are.

Find an instance where XLR line out is not immune to P48 and I may agree with you.
But – you won’t, because standard design mandates it to be DC blocked (with caps) or isolated (transformer). To make it idiot-proof.

Don’t lick connectors! It’s not hygienic, it corrodes contacts.
If you develop a habit and lick a wrong one it may end up being lethal

I have to disagree your comment “The whole re-inventing-the-wheel debate is moot if you don’t use cable adaptors EVER.”

Two comments:
1. In very many real live audio applications, especially on temporary setups, you need to use adaptors here and there to get the show running.
2. Using just same type connectors to same type connectors does not guarantee that things always works as planned. I have damaged equipment with XLR to XLR connections where someone accidentally left on phantom power.

“There are valid reasons we use standards to make things work”

There are valid reason to have standards and use them. Unfortunately there are many incompatible standards, different manufacturers interpret then differently etc..
Follow standards when you can, and when you can’t you need to adapt and overcome- or cancel the show.