When you’ve been at work for 1 minute and someone comes in to dump a massive turd of a problem on your desk. 

THAT is the perfect time to say “not until I’ve had my coffee” because it buys you some time to reflect on your life choices, if you NEED the job, and then conclude it’s not the worst thing, it’s just not a great way to start the day.

 “I need my coffee” is just a buffer to prevent your day being started off on the wrong foot.