Weird = ?

Hmmm... Verticillium wilt??? Plagues maples, but usually under hotter and wet conditions. That's a head scratcher.

but usually under hotter and wet conditions

Not necessarily. Stress of any kind can encourage the incidence of verticillium and we are seeing a lot of winter killed young JM's in my area that have VW. As well as those that began to leaf out this spring but then rapidly failed. Unusual weather conditions - like much of the US experienced late winter and early spring - could definitely be a factor. Although not as common in container grown plants as it is with those planted in the ground, it can happen.

The rapidity of the decline could indicate VW but other pathogens can have a similar symptomology. Diagnosis might be best accomplished by taking a sample to your extension office pathologist or other qualified source.

Our Japanese maple is approximately five years old. I have always cut our grass, but this year hired my neighbor, "a landscaper", who stripped about 1/2 the bark around the trunk using a weed whacker (FTLOG). Over the last couple of months, there has been even more loss, so total loss is a 2-3" tall x 75% circumferential band of gored trunk. First one major branch, now all over, the leaves are curling and browning at the tips. The leaves are not the right color for this time of year. I left it alone thinking I would invite disease by bandaging, but now I think it's failing. Any suggestions? I am very upset. I warned him about this, but he did it anyway. This was a beautiful young tree, now it appears to be losing its struggle to survive.

Sucks, especially since the fella who did something wrong is your neighbor and you will have to see him in the future.

It is fall. Any chance of posting a picture using a site such as photobucket? You say the tree is losing the battle to encapsulate the wound?

Still I am not optimistic about your tree. Any sprouts from below the girdled point?