At our house, mullygrubbing always meant feeling sorry for oneself, being in a blue funk, morose...a GrubWort, on the other hand, is a very dirty little kid, usually with sand/ dirt/food, etc. stuck to his face and hands
She had been mullygrubbing all day, complaining and scowling.
The little GrubWort left tracks all over the kitchen floor.
In North Staffordshire - England, "Mullygrubbing" is a form of punisment, usually given by an older brother to a younger sibling. A kind of bullying. To mullygrub someone you must get the victim into a position whereby there head is clasped between your upper-legs, face forward, scalp to you. Then you rub your knuckles agressively into their hair for several seconds - even a minute or two has been known. Ask my younger sister!
Melanie you twat! For nicking my fireworks I'm going to give you a jolly good mullygrubbing!