Molly Piss 

British slang, originating in Plymouth, Devon, it means an ineffectual male. The epithet also implies that the recipient is also moronic impotent, effeminate and incompetent. The origin is believed to derive from the expression 'not worth a Molly's piss', where Molly or Mollie was a slang name for a prostitute. So a Molly Piss is someone who is not worth a prostitute’s piss, meaning that they are of no account or totally worthless.

“Mark’s all uptight and emotional because Terry pointed out a fundamental error in his figures, says he’s going to resign because he can’t take the constant criticism.”
“What a molly piss!”

Molly Piss by AKACroatalin June 5, 2015

Molly Piss 

British Westcountry slang for an ineffectual male. The epithet carries with it implications that the recipient is also impotent, effeminate and incompetent. The origin is unclear, perhaps deriving from the expression 'not worth Molly's piss' meaning to be of no account or worthless, although who Molly was we'll never know.

Malcolm's got all emotional again 'cos he can't get the computer to work, says it's something technical.
Did he plug it in?
No, but he threatened to raise a grievance against me 'cos I laughed at him!
What a Molly Piss!

Molly Piss by Croatalin November 24, 2013