If I'm out and about and there happens to be someone nearby talking loudly (usually on their phone), then I'll often pretend I'm taking part in the conversation. The beauty of this is that the other person is so wrapped up in what they are saying that they don't realise I'm right next to them taking the piss.
Today, I was taking a gentle stroll along the seafront with Julie. We had just crossed the road, and were passing a couple who were discussing something or other. As is so often the case with even a quiet conversation, odd words or phrases float out and catch your attention. This time, though, Julie was there and was talking too...
Wait, what? I stared at Julie, and asked why she thought the woman we had just passed would have been concerned about a local sporting event.
As it turned out, Julie hadn't intended to give this impression. She just happened to comment upon a sign at precisely the moment the 'concerned' woman move out of earshot.
And confused the hell out of me.
If you want a true masterpiece of talking at cross purposes, though, you would be hard-pressed to find a better example than this clip by comedy duo The Two Ronnies.