a person, usually male, that masturbates a lot. The bishop in this case being a euphemism for the penis.
Joe's a proper bishop basher, he was lying in bed the other morning bashing the bishop with his headphones on and when he finished, he noticed his mum had been in and left his tea and toast beside his bed.
He was bored so he put on a porno and bashed his bishops helmet off. What a bishop basher.