Halfwit
A baniak is a pejorative slang term for a fool.
Galah, mug, yarra, dingbat.
Blockhead, bonehead, twit, nincompoop
That might be OMG.
The only deffiniton of Gommie I know of is that it's slang for a fool.
Drongo, galah, mug, yarra, drop kick.
try urbandictionary.com
Its a British slang term for a fool or a person regarded as insignificant and contemptible. an annoying person
Yes, in an informal letter it is OK to use slang.
to bamboozle = to fool The four letter word for bamboozle is fool.
In rhyming slang, "melt" is used to mean "idiot" or "fool." This slang is often used in British English and derives from a phrase that rhymes with the word it represents, like "melted cheese" rhyming with "idiot" in this case.