When a person is being bratty, childish, annoying either because he/she is not getting his/her way, is feeling tired/hungry and acts up due to one/all of those circumstances.
Synonyms of necio are bratty childish immature annoying fussy
Used in US as well
"He was being a necio because he wasn?t getting his way. The baby is necio/necia because he/she is hungry/tired/sick."