Possible Clues:

• Whisky perhaps diluted gets you easily riled
• Getting too upset too quickly
• It's little irritation for writer to cross
• Electrical fault moderated, but liable to blow a fuse
• Impatient
• Being easily riled, loses the head on drink with Peter M. Cook in outhouse
• Shattered stepmother rose thus?
• By the sound of it, Kurt is fortified in a steely way - is that why he's like a bear with a sore head?
• Irritable as spirit diluted
• Easily made angry