Imagine you go up to the bar. There are two people waiting there. After they get served you think it should be your turn. However somebody else comes up and gets served before you, despite not having joined the 'queue'.
At what point do you say to the bar staff or whoever is getting served ahead of you 'aherm actually it was my turn thankyouverymuch'? After the first person to be served ahead of you? The second?
Conversely, if you realise you've skipped the queue, do you point it out and let somebody else go ahead of you?
I'll reveal the correct answers later.