Friend's iMac finder not responding because of failed massive drag and drop?

[Onamuji]

The bottleneck is where the Finder is trying to draw a thousand or more Desktop icons.

Boot from an external drive, open a new Finder window in list view and browse to his Desktop folder. Make a new folder and drag the entire contents of his Desktop folder into the new folder.

With his Desktop clean, everything should be back to normal.