Grump-a-dump is a name for a person that is tres grumpy. Can also be known as a grumpasaurus!
A "grump dump" is when a person or place is really down in the dumps. When one is not feeling good and is just grumpy all around.
Person 1: ugh, I hate math class!
Person 2: ay stop being a grump dump at least we don't have a test!