|B: too Busy||When task assigned||I’ve got too much on my plate, what can we take off to make this fit?|
|F: I Failed/We're F@#$'d||When task becomes a failure||I couldn’t get this done, now we’re screwed what would you like to do.|
|Q: I Quit||When burned out||I haven’t seen my family in weeks, my fish died of starvation - I quit!|
Even if you're not yet in task overload think very hard about which conversation your boss would rather have. If your boss would rather conversation F or Q, you need to find a new job(+).
I'll assume after doing the previous mental exercise you're not out looking for work, so let's ponder how to have conversation B. Clearly your boss didn't give you a task because she was bored, she needed the work done. Bring your boss your current prioritized, costed, task list, and try to fit the new work into it, recommending where the new item should fit in the task list.
At this point, your boss will agree with your recommendation or work with you to change your prioritization to keep you under a realistic work load.
ps. To my surprise some people I respect disagree with my approach and think I'm being naive. They claim that having conversation B shows you are weak, and will put you in debt with your boss. If you think conversation B is not the way to go, put your thoughts in the comments.
(*) Depending on your circumstance boss may be a euphemism for: partner, wife, husband, significant other, parent etc.
(+) Depending on your circumstance job may be a euphemism for: relationship.