I'm a What?

I admit it, I've been a little crabby the past few days. Gabe is sick and needy and I'm tired and concerned. Well, I guess "a little crabby" translates into much more when you're young. At the lunch table today I gave a rather short answer to a stupid question and Shane said,

"Man, you've been a grouch for about a week now!"

Lisa asked, "What's a grouch?"

I was trying to use adverbs like fussy and pouty so she would 'get it' when Shane chimed in,

"It's like an old brat."