Pronounced in its home town of Glasgow
as 'Yer Jaickets oan a shaky nail' this phrase is commonly used to inform people that they have, or are about to, step over the line.
Most often this phrase will be used by mothers or SOs to inform you that whatever you are doing or saying is not appreciated and that they wish you to desist or change your ways.
The symbolism is fairly easy to understand. You have hung your jacket up on a nail in the wall instead of a hanger. Said nail is not firmly smacked into said wall and may at any point fall out, taking your jacket with it. i.e. You are basing your actions on a mis-placed feeling of security in your relationship and this security may crumble at any point, taking you with it.
He: I'm just off out the pub with the lads, be back whenever. Don't wait up.
She:Yer jaickets oan a shaky nail, son, get back in that kitchen and finish the dishes.