A person who insists on engaging others in lengthy conversations whilst simultaneously speaking with a total disregard for both diction and appropriate use of volume. In effect taking the act of simply mumbling and elevating it, by way of conversational persistence, to a level of cuntishness. Therefore becoming referred to as a mumblecunt.
Hey Dave we should get going, Terry's coming this way and he's a right fucking mumblecunt.
"When a person makes minimal effort to sing along to a song on the communal radio. It is loud enough to hear, but not clear enough to distinguish the words, therefore this person is the most irritating in the office environment.
Originally spawned from distaste over the replacement of the original actor who played the lead wizard in the popular set of books by JK Rowling. Richard Harris (RIP) WAS Dumbledore, but Gambon is DumbleCunt! Now used as an insult to anyone who is a total knucklehead.