Thou.

[RiverNotch]

The archaisms do make this twice as disgusting, and not in a good way. One could send this as a somewhat effective insult to another -- and at the same time open an avenue for a retort. "Thou" doest naught -- modernize him. For this reviewe, I do.

You are the bastard of the apple,
Seedlings of the God bollock, When I read this, I immediately thought of something, well, symbolic -- that is, we all are seedlings of God's bollocks.
Farts from the steam whistle,
Reminding you to forget. This last line, and to be honest this whole stanza, really gave me nothing -- the insults didn't immediately and clearly register.

You are a busted flush, Comma is unnecessary.
Of the card table,
Of the lavatory,  
The house has your money,
But you get to keep the turd. This whole stanza, though a bit clever, made me go all "meh". The second and third lines gave the game away -- remove them, and maybe this'll get better.

You are junk food, Instead of comma, colon -- the following flow from this.
Your mind is Kentucky-Fried, The capital in "Fried" is unnecessary.
Your soul is flame-grilled, I know this is a reference to Burger King (or at least, I think I know), but anything grilled is, if not over or under, good. Not sure if you should change this.
Your flesh is a stuffed crust,
And your nuts are dry-roasted. Not really junk food, but I laughed at this one.

In fact, though the insults are sometimes brilliant, they're really just that, insults. We could comment on the form and the choice of imagery, but as a poem, this didn't really give me anything worthwhile.