Barking mad
Definition 1 of 2
Pro Tip 1/3Exaggeration
Expresses extreme behavior; not always literal. 
He's barking mad for collecting stamps, but he loves it.
Pro Tip 2/3Slang Usage
Used informally, not suitable in formal writing or speech. 
I felt barking mad when my computer crashed again.
Pro Tip 3/3British Origin
Mainly used in the UK, might not be understood elsewhere. 
Mum's barking mad for that British detective show.