I'm a generally calm, placid intelligent professional woman and life usually ticks along nicely and without major trauma.
But every 6 months or so someone gets to me - perhaps a relative or someone in a shop and I behave in a way I don't want to behave. I storm off (no shouting or swearing) and then feel ridiculous that I couldn't deal with the situation better.
It happened last week - I'd bought an expensive piece of equipment and the store were meant to be showing me how to use it. Instead the assistant said this is what we'll show you, we can't show you that (what I wanted to know and what the sales guy had promised they'd show me) so I stormed off after saying they could keep the item as it was useless to me if they couldn't show me how to use it as I wanted. But then I had to go back as I'd already paid for it 
Really I just want some advice on how to deal with annoying tossers irritants better than this. How do I stop that 'stand up and walk out' response that just seems to happen?
Sorry, I know this is petty and insignificant compared to others troubles.