I posted on here a month or so back about my nerves as a new driver - everyone was very helpful and I am feeling much better about it all now! I was wondering if I could ask for your thoughts on a situation I found myself in this afternoon.
So, I'm approaching a mini roundabout (purple car in the picture!) turning left. To my immediate right is a one-way street (feeding onto the roundabout) that is very rarely used. Opposite me is a big queue of cars, turning right, so aiming for the same turn-off as me. My understanding is that in this situation (where you're at 180 degrees to each other) the first car to arrive has priority, so I let the "blue" car across from me go ahead. The problem is that all of the other cars behind that car then proceed to follow it out onto the roundabout - I think a lot of drivers tend to 'ignore' the one-way street at that roundabout and therefore assume right of way over people opposite them.
Then the traffic lights for the pedestrian crossing (the red lines on the picture) turn red, so the cars that have pulled out get stuck on the roundabout - there's no space for me to pull out at all. The traffic lights turn green and as they start to move on I wait for a moment to see what the remaining car on the other side of the roundabout is going to do - it's a mini so if it were a larger roundabout I'd have pulled out as there'd be time for me to turn before they reach me but I'm wary of there not being enough space if they assume priority. They hold back to let me out and as they do, the car behind me honks really aggressively (not a "toot toot, you can go", but a "MOVE!" kind of honk if that makes sense) and as I look in the mirror the driver behind me is waving his hands really angrily.
As I pull out I toot back (not as loudly) and stick up my finger. 
I think I probably WBU to get angry/upset in response, but was he BU to honk? I don't think he can have been waiting behind me for more than 30 seconds, and I didn't particularly want to bully my way onto the roundabout. What do people think (and what would you do on a roundabout where priority isn't obvious / other drivers are assuming priority)?