I also don't know if anyone ever popped their cheeks to Cyril Poacher, but the USAF airbase crews who went for a drink in the Ship used to strum their guitars while he and the others were singing - and generally what the former were strumming was not what the latter were singing - to the point where it was very difficult to get him to sing at all.
Also I have mentioned on another thread the story that Bob Pegg once saw Harry Cox performing at a Norfolk folk club, and every time he tried to sing, someone with a reel to feel recorder practically shoved the 'lollipop' up his nose. When Bob complained, the response of the MC was 'It's alright. It's only old Harry. He doesn't know what's going on!'
In fairness I should say that some of the old boys were known to get their own back. Fred Jordan for one had a line in asides the loudness of which was, I suspect, not always directly attributable to his declining hearing in later years. I was once the patsy when someone had sung 'One too many mornings' and Fred turned to me and asked not very quietly 'What's that, boy? I haven't heard that before.' (Me) 'That's by Bob Dylan' (Fred) 'Oh that's why I haven't heard it, see!'
And whilst I don't hold him in quite the same catagory as the above, let me open a floodgate: please write in, all the people who were ever interrupted/halted in their performance by helpful comments on their technique by Ken Loveless.