To get a waiters attention by clicking is considered rude.
Why?
Nobody could tell me but everyone agreed it shouldn’t be done.
It seems to be widely accepted as a social no no without a known explanation.
To put a gauge on it, it’s somewhat ruder than the eye contact with a raised finger and definitely politer than shouting.
To throw my hypothesis into the ring I think that the click is rude because it has an air of pomposity.
I think that people associate it with the upper class summoning their servants and no waiter wants to be considered a servant.
Thomas Duggan 