Napoleon once opined, "When people cease to complain, they cease to think."
The British love to complain, but we're not very good at it - our natural reticence and desire to avoid confrontation makes complaining challenging. Although we like a good whinge, we're more likely to moan at someone else than complain directly, through the proper channels or in a way that might actually fix the problem.
At this moment in a restaurant near you, there is a familiar scene - a couple huddled together, comparing how salty their soup is, how cold their kedgeree, when a waiter approaches. "Everything all right here?" "Oh yes, fine, thank you."
At least this form of complaining isn't rude, because its target never gets to hear the harsh words we are having such fun delivering. If, however, you want to complain in an effective way, there are ways and means of doing so politely that will avoid temper, high blood pressure and shouting - never the best way to achieve your goal.
Always pay lip service to calmly following the proper channels, and only when those are exhausted, do you smilingly ask if it is possible to see the manager, while making it obvious that you're not leaving until something good happens.
Try if at all possible to resolve the complaint there and then rather than being fobbed off by the advice to write a letter. Remember that your adversaries are often trained in the art of 'customer service' (a.k.a. anything but) so they are skilled in complaint deflection strategies.
Rudeness merely activates these strategies, whereas politeness and an eagerness to work with them to solve your problem are often disarming. Sometimes all you have to do is smile confidently and say, "I'm sure we can resolve this," or subtly remind them of the reputation they have to uphold.
At all times, out-do any saccharine obtuseness with extra dollops of twice-as nice from you: you will reap sweet rewards.