Usually, to avoid any ambiguities, I'd say 'waiting in the queue', however I came across 'sitting in a queue' and wanted to know whether it's correct or incorrect English.
Is it used? And if yes, in what context/s?
I'm from the UK and "Sitting in a queue" is a perfectly normal thing to say.
Sometimes the word "sitting" can be used to mean "staying in one place" (like you might sit an object on a table). In this sense, people might say that they were "sitting in the queue for hours", even if they spent the entire time standing up: "sitting" in this usage means that the queue was moving so slow that they spent extended periods of time not moving at all. Also, of course, they might mean that they were actually sitting down: this might refer to the type of queueing system where you take a ticket and sit down and wait for your ticket's number to be called.
The phrase "sitting in a queue" is also often used to describe inanimate objects, or even virtual objects, such as emails, helpdesk tickets etc. For example:
"Did you deal with that purchase order problem yet?" "No, it's been sitting in my queue since tuesday"
There are two common types of queue I am often in - people in a line (eg at the bank) and cars on a busy road. Usually, saying that I am in a queue implies that I am (of course) waiting. So usually I would not say that I am 'waiting' in a queue.
When it is a queue of people - I'm in a queue/ I'm queuing (waiting is understood). Or, I'm in a queue waiting ... (to be served). If the queue is moving too slowly you might say I've been stood/waiting in this queue for ages.
When it is a queue of cars - I'm in a queue/ I'm queuing (waiting is understood). Or, I'm in a queue waiting ... (to join the motorway). If the queue is moving too slowly you might say I've been stuck/sitting in this queue for ages. (NB In a car I would not ordinarily say that I am 'waiting' in the queue).
Sitting in a queue is definitely proper english when used in proper context. however a good look at the definition for "sitting" and "queue" Straight from the Oxford Dictionary is a great idea as some usage may not be suitable nor proper english.
Sure, it's correct. You need not be resting your derrière on a bench or chair to be sitting.
See, for example,
That said, standing might be a better word, particularly if you're standing upright, and only in the queue for five minutes or so. But sitting is not (to quote your title) "incorrect English."
If, for example, I was waiting to see a doctor -- where there's a queue (even with appointments, since the doctor almost always runs over time) and those waiting in the queue will be actually sitting waiting for their turn, if I was talking to someone on the phone I might say to them "I am sitting in a queue".
But if I was standing in a queue, I wouldn't normally describe that as sitting (I consider it if I was trying to use the word "sit" in a slightly different sense, that of being situated in some place -- but I'd usually tend to avoid it in this context, not least for the hope of avoiding ambiguity).