One of my pet hates is uninvited 'joiners-in'. Fairly recently I embarked on a ballad at a singaround and soon realised that the bloke next to me was singing along with me quite loudly! I had to stop and remind this person that my performance was not a duet! On another occasion, whilst I was singing from a stage, someone in the audience joined in in a completely different key ...

In my opinion ballad interpretation is a very personal thing and joining in is very bad manners.

People who insist on dictating the rhythm and pace of a singer's performance during refrains and choruses are also, imo, displaying crass rudeness.

Personally, I blame all those 'folk choirs' of the 60s and 70s who made people believe that 'dirgey' bellowing and harmonising are 'de rigeur' and must be indulged in at every opportunity.