1. The most common thing that drives everyone – from London, on holiday, even just visiting from out of Central – crazy is those select few people that just don't care when it comes to London Tube and Bus manners. Due to how it annoys and affects everyone, not just those behind but left, right and centre, it goes first on the list. Nothing is going to cause such a cry for blood as ignoring these basic rules; don't queue jump to get on public transport, let the passengers off first before getting on, holding up a lift, or standing on the walking side of an escalator. These are all dangerous things to do because natural Londoners don't just tut anymore – they'll push you out of the way quickly and without warning, then mutter as they go.
2. Similarly walking in large groups at a very slow pace is a sure way to enrage all those behind. Most people accept that not everyone has seen Big Ben three-hundred and sixty-five times, but leave some room between you and the road so others don't have to jump into it (and risk irate cyclists and Black Cabs) to get around. London Streets are notoriously difficult to navigate but observe the flow of the pavements; they do have their own naturally occurring one-way systems.
3. Related to crowds is the dreaded "tourist meets" that tend to happen in the middle of the pavements or directly in front of the Underground exit and/or road crossings. It isn't so much that it will drive the people behind nuts, but more that it is frustrating to walk into a large crowd and then once fighting your way to the other side, ending up in the middle of a road, directly in front of a double-decker bus.
4. Mentioning roads; don't, whatever you do, dash across them without looking, or before the green man, or just directly into oncoming traffic because you "think" you can make it. London roads are just as lethal as the pavements and as someone who has grabbed several people by their suit collars or hoods, I can't promise that everyone standing behind you will do the same.
5. Just like with understanding how the rules – or lack of them – work on the roads and pavements, make sure you know the rules of the famous icons. No, not the landmarks but the Royal Guard, Mounted Police and various other Ye Olde Attractions of London. Don't pet or feed the horses, don't laugh at the Beefeater, don't try and make the soldier move. In general be respectful and observe what not to do by watching the people in front. I can guarantee there is almost always someone about to get bitten by a horse. But please, if you want to get bitten or very curtly told off/removed then by all means do. You'll give the people around you something to laugh at.
6. This one goes out to everyone that has to use public transport, particularly London Underground; if you ever get that urge. That super strong urge you just can't stop or avoid, please, pleaseplease cover your mouth when sneezing/coughing. It makes everyone flinch, especially if they are in front of you as opposed to getting acquainted with your back and elbows.
7. Talking of limbs; don't point suddenly to the left, right, in front or behind. In fact don't point at all when walking through London. I've nearly lost eyes because of other people's sudden excitement.
8. Another act that will upset those walking behind you and drive them nuts is stopping suddenly to do something (look inside their bag, checking out a shop window etc.) from the middle of the pavement. Sometimes it really is just easier to navigate toward the side of a building than simply stop and nearly cause was walking pile-up.
9. This one should be pretty standard; please don't chuck litter to the side when you are done. Just find a bin. There are now plenty in London, especially recycling bins because of the amount to trouble slipping/tripping on McDonald's wrappers was becoming.
10. Finally, and similarly to the use of bins; don't feed the pigeons, especially outside of restaurants. There is nothing is worse than walking into a flock of descending pigeons after their next meal. The people behind you do not appreciated dodging winged rats or being their next poop-target.