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1.
A word for people that have brown hair but act in a way associated with blonde people.

For the record - the way you act has nothing at all to do with your hair colour. It's just a slang saying I hear a lot.
My mate's malteaser, she picked up a clump of nettles, her explaination: "I thought they were my bag"
by Evil_Bob [The Female] December 30, 2004
 
2.
A brunette girl, but with a very blonde mind. Therefor being brown on the outside, blonde inside.
Shes a total malteaser, brunette but thick as a blonde
by rona8z November 22, 2009
 
3.
a girl ( or boy ) who is a brunette/dark haired person who does stupid things, or has "blonde moments"
eg, a brunette walks into a glass door! everyone calls the brunette a malteaser as she had a "blonde moment" cuz the brunette is dark outside but blonde inside just like a malteaser
by maryanne bob May 04, 2007