People who say "0207" and "0208" really piss me off
There is a single telephone code for London: 020.

It has been 15 YEARS since London were split up into "central" and "outer" telephone code areas. We used to have 0171 for central London and 0181 for outer London. However 15 years ago they unified London into just one telephone code, and extended the local number to 8 digits instead of 7. For example:

(0171) xxx xxxx became (020) 7xxx xxxx
(0181) xxx xxxx became (020) 8xxx xxxx

That was for the older numbers. But nowadays London numbers may be assigned with a 7, 8 or even a 3 - ANYWHERE in London. There is no longer any geographical significance in any split. If you don't believe me, test it: from one London land-line to another, whose code is (020). You don't need to dial the 020: just start dialling the local number.

Yet still you see signs written, newspaper adverts, office workers repeating their phone number as "0208 ....".

Stupidity annoys me.
(EuroSong I love horse meat: best of all the animals, Mon 21 Mar 2016, 11:37, 11 replies)

this wins the award for being the dullest thing to be annoyed about
in the history of the universe
( Grrrmachine the indifference engine, Mon 21 Mar 2016, 11:40, closed)

No duller than people getting annoyed about (h)aitch, or minor grammatical mistakes made by others.
Fits the question quite nicely actually.
(EuroSong I love horse meat: best of all the animals, Mon 21 Mar 2016, 11:53, closed)

I dunno, I find you pretty annoying at times.

( 2 Can Chunder Word to your mums, I came to prod bums, Mon 21 Mar 2016, 11:59, closed)

fucking hell

( The Doveston haunted by the memory of his own amnesia, Mon 21 Mar 2016, 15:44, closed)

^

( Slippery Mick ‏, Mon 21 Mar 2016, 23:19, closed)

Agree
( Ken Oath, Tue 22 Mar 2016, 11:08, closed)

i tend to lump in the 5th number into the beginning
so it's 02081 234 567
that way it aligns with the national format 01234 567 890

so stick that in your pipe and smoke it
( mictoboy shitting in your cunt since, Mon 21 Mar 2016, 20:30, closed)

C'MON CALL CHATBACK!
0891 50 50 50
(eViLegion Chief Commissioner of the Scottish Lunacy Board, Mon 21 Mar 2016, 20:39, closed)

Bang on squire. As anyone involved with the original phONEday migration from '95 would know these things are important. I was there man!

Details matter.
(BrontoChorusBob, Tue 22 Mar 2016, 21:25, closed)

NO-ONE CARES

( drimble he'd been white, he'd been black, Mon 28 Mar 2016, 8:07, closed)