i Register
In some senses, grumpy is marked as informal. Watch for register when choosing this word.
adj
Dissatisfied and irritable.
The old man was grumpy because he couldn’t find his glasses.
noun
A dissatisfied and irritable person.
"Bunch of grumpies, always scowling and muttering," complained the new employee. "Dear me, I'm afraid you'll find the same type of people here," the foreman responded.