• noun (pl. barneys) Brit. Informal an argument, a noisy quarrel.
— ORIGIN of unknown origin.
To "have a barney" is a phrase commonly used in London.
It means to become involved in an argument or fight (and has no connection whatsoever with any kind of purple dinosaur).
The origins of this phrase appear to be Cockney, dating from around the 1850’s, but it is also commonly used in Ireland and Australia. I cannot find any evidence that Barney refers to a particular gentleman named Barney.
I can tell you however that it has no connection to the Cockney Rhyming Slang …
Barney Rubble Rhyming slang for ‘trouble’</b>
which obviously derives from ‘The Flintstones’!
Dave got into a bit of a barney dahn the pub
Dave’s lies are always getting him into barney rubble!