Used by Eegra in their valentines day comic, where Bowser handed Peach a card with this phrase, and subsequently believes it is a sweet love message. Or something. Whatever the case, it's an exclamation yelled at a loved one that expresses ones awkwardness in a social or romantic situation.

a phrase chiefly used in northern England.

it is a contracted form of "it'll be reet", where "reet" means "alright" or "OK".

living your life according to "be reet" is the only way to find happiness in life.