Also, I have just remembered...
Every second or third time I go into my local post office, they try and sell me insurance. Car insurance, pet insurance, holiday insurance, house insurance, home contents insurance. 'I am fine with what I have got actually... honestly.' 'Yeah but I bet we can better it!' 'I have just signed up for 12 months insurance on my car last week. 'We can pay the cancellation fee for you.' 
They just won't quit, so I have lost count of the amount of times I have taken the info, (and made an appointment even 'chat' to someone' which I have cancelled!)
Also, every time I go into Wilko's. (great shop, friendly staff, but...) every time I go in, they give me some spiel at the end of the transaction about how I can win £250 worth of goodies if I fill in this online survey. It literally IS so they can get your personal info.
I am also sick of going into Asda and have them asking my postcode (so they can see how far people travel to their store apparently.)
I give a fake one of course. I always give the one of the community centre 10 minutes walk from my house.
And is it just me, or does anyone else think it's odd that Starbucks want to know your name, so they can 'put it on your cup?' 
IMO the 'annoying thing that trumps everything else' HAS to be the insistence that you take additional breakdown cover/extra guarantees.
DH and I had quite the 'debate' with a certain major store the other week, when they tried to sell additional cover for a £9 mp3 player. The MP3 player was £9, and the additional insurance was £5. DH said 'are you serious? It's not worth it.' 'Yeah but if it breaks and you bring it back, we can replace it completely.'
I said 'you have to do that anyway, under the normal 12 month guarantee! If I lose it after 13 months, I don't care, it's nine quid! We spent that in Costa yesterday on 2 lattes and a cake each.' 'Yeah but it covers accidental damage.' I said 'Our house insurance covers that.'
They went on and on and on. We said 'look, we know you get brownie points for selling extra insurance, but we're not taking it. Can we just pay for the MP3 player now, or shall we go somewhere else to buy it?' Cue the assistant shutting up, and selling us the item after wasting five minutes of our precious lives trying to sell us extra shit we didn't need or want!
Why the F do they get rewarded for selling insurance no-one needs? very annoying. 
I predict that one day, there will be a fuck load of claims from people claiming they were mis-sold additional insurance plans that they didn't ask for, for items they bought! It HAS to happen!
(And yeah I KNOW it's not the fault of the assistants, but this particular one got quite arsey when we wouldn't take the extra insurance, that cost more than the fucking item we were buying!)