Prompted by a few remarks in the "manners" thread and elsewhere recently.

How have people dealt with club or session regulars losing the plot?

Outright psychosis is maybe one of the easier ones to deal with - I've seen one person brought into an event by a friend while having some sort of acute rapid-cycling bipolar episode. Friend must have thought it would be good for her, and it might well have been, except that performing through somebody alternately shouting encouragement and bursting into tears isn't easy. (She was once a valuable asset to the folk scene, and I think I'd have done the same as the friend in his position. He couldn't have known what would happen).

Then there's the person who was once a good singer but is in terminal slow decline, unable to remember the tune most of the time, forgetting the words for nearly every song, and unable to read their own cheat sheet.

Alcoholism is probably the commonest problem folkies run into, but in my experience drunks tend to just stay away when on a serious bender (and others can go on performing past the point of being able to stand up). With drugs I suspect E is the worst in this setting - people get into foul tempers coming down off the stuff.

Events in pubs always have the easy option of getting the publican to ban people but that may not always be appropriate.

Anyone had to deal with somebody having established, persistent delusions, as from paranoid schizophrenia?