It suggests someone who is easily annoyed, unhappy, and likely to express their dissatisfaction in a grumpy or unpleasant way.
Here are some synonyms for grouchy:
* Grumpy
* Crabby
* Sullen
* Cross
* Peevish
* Ill-humored
* Surly
For example:
* "The old man was so grouchy that no one dared to talk to him."
* "I woke up feeling grouchy this morning."
* "Don't be so grouchy! It's a beautiful day!"