It is worth remembering that stalling is not against any road law. It is an unfortunate part of driving that everyone experiences from time to time. Using the horn however to show frustration at people who stall, is against road law. Your horn is there to make others aware of your presence as a last resort, not to show how peed off you are at being made to wait a bit longer at some lights. So let them pip the horn all they want. Your doing nothing wrong in the grand scheme of things...they are and those who use the horn deserve to wait in my eyes.
However, I would personally practice stopping and starting in a quiet area and get used too it as much as you possibly can. The worst case scenario is that you stall in a narrow and busy area and hold up traffic with an ambulance or fire engine trying to get through behind you. Besides...stalling once is fine, twice if your new to driving, is understandable. But to stall over and over again, especially on a flat makes it pretty obvious that you need some practice and shouldn't be amongst heavy traffic yet. Remember, just because you have a full driving license doesn't necessarily mean you can drive like every experienced driver on the road. You will become more experienced with every hour that goes by as you become more and more used too it.
And a message to all drivers out there who pip their horns at people who stall...think about what you are doing. Stalling at lights, especially when its busy is a pretty embarrassing thing to do and can rattle a persons confidence meaning they are much more likely to stall again on the second attempt because they now feel the pressure of having to be quick and make up for lost time for the traffic behind. The last thing they need at this point is some inpatient prat pipping their horn behind them and making it ten times worse. As I said, if you pip your horn, you deserve to wait in my opinion. Bare in mind that it could be a new driver with his or her first car. Imagine it is your son or daughter or mother or father or someone you care about. Give people a break on the road sometimes, you don't always know who is behind the wheel and why they are stalling or going slow on roads. Another thing as well...why do some people think it is okay to speed past and overtake learner drivers or drivers traveling any slower than the speed limit...ITS NOT OKAY! Nowhere in the highway code or any book of road law does it say that you can overtake people at 40mph who are traveling 28 in a 30 zone or if they have L or P plates on. The amount of people who are always right up close behind learner drivers and just passed vechiles. Get these idiots off the roads. Rant over.