brat baby 

Someone of the age of reasoning (ie. older than 12) acting like a spoiled child. (ie. pouting, throwing a tantrum, etc.)

Patrick was just being a brat baby, he was angry he had to work while his wife got to stay home with the children

brat baby by Jennifer Severson July 5, 2008

Beanie baby brat

(Noun) bean·ie ba·by brat

/ˈbēnē/ /ˈbābē/ /brat/
1. A derogatory term for when you're younger sibling is being an absolute twat waffle.

2. When a younger sibling doesn't understand the hierarchy. (IE: Someone who is unable to comprehend thr birth rights of the much older and wiser sibling)

3.Gavyn with a Y instead of an I

"Wow Gavyn is being a beanie baby brat."

Beanie baby brat by Slashlite August 26, 2022