In English means: "Dumb... and (still) walking". It is used to describe the foolness of a person who is completely unaware of what is going on around him/her. e.g.

Person 1: "Check out this car which just got out of the gas station!"
Person 2: "OMG! the driver took off with the gas nozzle still inside!"
Person 1: "...and he has no idea"
Person 2 (laughin): "ghecheh w mecheh"