When we say "you're certainly taking your own sweet time" we mean that the person is completely ignoring any urgency placed on the matter by others. The person is doing when he wants to do it and not a minute sooner. I suppose it's a sarcastic use of "sweet." I hadn't thought about it until you asked the question.
I'll be interested in seeing what others have to say about it.
Usually we use the term, "Someone is taking their sweet time," when maybe they're stopping to smell the roses, and we want to hurry to get past them. Usually it's a sarcastic saying that infers that you are a bit impatient about their patience in how things are going....
muscott....you mean like this...
"Hey, come on...it's my turn. Don't smell the roses for too long. I'm waiting!!"
You gave me its picture in very 'clear' and 'funny' way.
JamesM, nichec...thank you too. 'wait' is very simple and clear synonym for 'take sweet time'. I've got perfect its meaning!