The term "plonkette" is used to describe a female version of a "plonker" and is a very light-hearted way to call someone an idiot , often used to people with affection, and when you call a woman a "Plonkette" you do so with a great big smile on you're face, and is completely non offensive.
Johnny. gosh you are making mistakes with your grammer again "You're such a plonker"
Angie , well me being a swiss dude and noticing you spelt GRAMMAR wrong !!!! Id say you are a "Plonkette" ;-)