Hi. I can see this idiom ("You'll be the death of me") is sometimes used, but what is this exact meaning?
You'll cause mischief (which I may come to regret, as it will affect me)
The mischief can be serious or less so; so the sentence can be jocular or serious.
Don't say things like that; they make me laugh but I know I shouldn't. You'll be the death of me.
The melting of the polar ice-caps will be the death of the Inuit way of life.
In the 'You... me' context the tone is likely to be jocular (though not always: 'You've been asking for more and more money ever since you left home - fifty quid here or there is OK. But £50,000? You'll be the death of me.')