OK, we had an issue some months ago. A certain person who had been attending our club (Its a session club really - nothing too formal)decided he was going to learn to play the guitar and sing. He managed to learn a few chords and cribbed loads of lyrics from the internet and proceeded to regale us with his reditions of some of his favourite songs. He was trying to run before he could walk, which is OK, many people do this and eventually manage, with help, to get there. This guy had a really poor voice, his timing depended on how difficult the chord change was. People did try to help him, one guy offered to pop round his house and run through a couple of songs with him. He would not accept any help or take on board any crittisisms.
It was bad enough when he was doing one or two songs per night, but he started jumping in at every lul in the evening and was doing up to NINE songs in an evening. Despite the fact that when he started singing people went to the bar, bog or out for a fag and when he finished there was little or very scant aplause, it was like water off a ducks back - good performers stopped coming, people who poped in as a one off heard him and never came back. Eventually, the landlord of the pub banned him form singing. Sad, but there you are.

I play and I sing at home, I don't think my voice is too bad, but I would not like to inflict it on others - some people just can't do it.