I won a set of NGK Iridium plugs for a "Letter of the Month" to Spannerman at AMCT a few years ago Pete, and had the same experience as you.
An expert here told me that Iridium plugs don't like the stock CB750 resistor plug caps, so I changed the leads for Bosch 8mm silicon leads and caps (Dyna 3 Ohm coils) and it made no fcuking difference, so they're still here, sitting on a shelf.
If your plugs are fouling due to a rich mixture (which you'll get if you set your carbs up as per the Honda manual, but with modern fuel) change them from D8's to D7's, and you won't have a problem.
Lastly, you need me to teach you about revenge. If someone wrongs you like that jerk did, follow him home by all means, but don't abuse him, ride past and go back at 3am and burn his fcuking house down, with him and his family inside.
If you can wait a few months, even better, with his attitude he'll have pissed off other folks in the interim, and he'll probably have forgotten about your incident. If he survives...........