It's a good note but, you explained all the reasons why you could not pull out of the side road, to him the only thing that was stopping him was you. This is how accidents, or "collisions", happen. One person is giving all round observation and the other is obsessed with one thing and missing all the other, like a red mist. I would of superglued the letter to his windscreen and then he wouldn't of missed it.
I was cut up once as I approached some traffic lights, they went red and we both stopped. Female passenger, male driver. He jumps out, well built bloke, looks like he could handle himself. I got out, my mate gets out, now the driver is on the back foot because he didn't know there was two of us. He stopped and looked, we too are a fair size and, just to add affect we are in uniform with our side arm strapped to our leg (unloaded but he didn't know that). I said "Yes?", at this point I think a little bit of poo came out and he jumped into his car just as the lights changed and shot of looking in his mirror.