Something old, something new...
A couple we used when I was a lad in North London:

In reply to almost anything, and using a variety of voices was "Tah!" a version of the american "Der!", but long before it came to prominance. We also used to say "Tish tish" if something went wrong, I believe it came from Faulty Towers.

One that I've been trying to get accepted for years is "an eighteen wheeler" to mean a really large pooh, as in "Phew, that was a real eighteen wheeler, I wouldn't go to the bog for a while". The term comes from the world of articulated lorries, and I think I first heard it in the film 'Convoy'.

My favouriter insult as a lad was "Dick breath", closely followed by "shit for brains"

Now (alas) I work in financial services, and a recent version of the 'one bottle short of a full crate' type thing was "He's a couple of percentage points short of the base rate"
(Che Grimsdale Best before:, Tue 3 Feb 2004, 14:00, Reply)