You: omg, that idiot riding the skateboard down that hill with no helmet is such a freakin' jackwaggon.
Me: you mean jackwagon?
You: no, I'm british.
Me: no you aren't.
You: shut up jackwagon.
A useless piece of equipment, usually military, used to refer to a mule-drawn freight wagon which had been pieced together from dicarded or substandard parts, and subject to frequentbreakdowns. Jackwagons typically were good for only one or two uses, then abandoned or discarded along roadsides and in ditches, and were often re-cannibalized to create new jackwagons.
"Maybe we should trot on over to mambypamby land and get you som confidence - you jackwagon!" Geico commercial