Left a TAFKAP era Prince Gig at London Arena (I think) as he was just jamming with the band (badly) and refused to play anything that sounded like a song, let alone one you might have heard of. Most of the audience were sitting down after about 5 minutes, and half had left by 30 minutes in.
Only other time was at a local heavy metal pub (Stick of Rock in Bethnal Green if anyone remembers it)where the lead singer was a girl in her teens who couldn’t sing in tune to save her life. The backing band (all men in their 40s) were great – I reckon one of them was her dad trying to give her a break, but she was so awful it hurt my ears.