If you have IBS you get a dreadful, painful, urge to go meaning you have to rush to the nearest loo - no matter how unpleasant it is - and once there, are literally trapped for as long as it takes ....
.... trouble is, it can take absolutely ages for anything to happen though in the meantime you get severe pain quite akin to contractions ... then you might get a bit of relief, but the pain tells you there's more to come so you sit there, and wait, and wait ..... until you eventually go again. And while this is happening you often feel terribly nauseous as well, sometimes to the point of throwing up.
This 'cycle' of 'stop and go' can take up to an hour - sometimes even longer. Believe me, it's the last thing anyone would want to do, stuck in a grotty, perhaps dirty, perhaps freezing cold, loo in that condition, usually all too well aware of the queue outside. It's even worse when it's a small space outside and maybe just a couple of cubicles - you feel humiliated and extremely self conscious with others waiting so close by. But can do absolutely nothing about it and the same must be true for others with bowel related conditions - many of which are far far more serious than IBS.
So apologies, and yes, if you're waiting to go and the queue is moving very slowly it's frustrating - but something like I've described might be one reason why. As others have said however, women's loos often need to have more cubicles - I can't imagine many women deliberately take longer in public loos than they need to - but sometimes that need is genuinely time consuming.