It's actually trivial, even with the best LLMs on the market:

Try to rapidly change the conversation to a wildly different subject

Humans will resist this, or say some final "closing comments"

Even the absolute best LLMs will happily go wherever they are led, without commenting remotely on topic shifts

Try it out

Edit: This isn't even a terribly contrived example by the way. It is an example of how some people with ADHD navigate normal conversations sometimes