The London Wave

If you drive in London you will know what this is. 
When that driver pulls out in front of you, causing you to brake, or drives up the outside lane and then pulls in at the last minute, rather than join the rest of you in the queue wanting to turn left.  Or when they take the last parking place by B&Q, which you had been about to reverse into, forcing you back out on the hunt for the nearly-ready-to-leave family along with seven other drivers, or when coming towards you along a narrow road they speed up to ensure they get to the most squeakily narrow bit first, forcing you against the pavement.
You get this desultorily handflap.  Palm outwards.
It says something like: 'Ha! I got there first. Ha! You were cowed and beaten, and I am the superior driver in all ways.  But just so as not to start a rumpus, I'm going to wave at you in pseudo-thanks, as though I am acknowledging your good manners, and expressing gratitude to you  for giving me a right of way I didn't deserve.  Even though we both know that's a lie and you didn't have a choice really unless you wanted to get aggressive, but by waving thanks I'm pretending it was all your decision. And covering up for your weakness and giving you a way out with a miniscule modicom of self respect.'
And you know what?  On really bad days you wave back.