Fred Dibnah, a famous englishman, is known for his many television programs on construction and industry, mainly from the industrial revolution period. His came about from his ability to bring down the great chimney stacks of the smoggy era. Sometimes brick by brick but more often dramatically felling them expertly to the ground to be cleared away. A 'Dibnah Dick' is either the loss of a perfectly good erection or it is the item/image that resulted in said flacidity. It can also mean something or someone being present that nullifies all possiblity of future erections. Similer to cock blocking
"Shit mate, condoms are a right Dibnah"
"ERGH DUDE! Get that ugly bitch out of here, she's causing such a fucking Dibnah Dick over here!"