Competently designed drip coffee makers have a simple device inside them specifically for people like Kevin. It's variously called something like "pause and serve," and what it basically boils down to is a little spring loaded plunger with a gasket on it that is pushed up by a knob on the lid of the carafe when it's installed. If you remove the carafe this closes like a little valve and water is allowed to accumulate inside the filter basket for some time, probably up to a minute or so, in order for you to pour a cup (or whatever else) in that amount of time before it finally overflows. It's simple, broadly effective, basically free to implement, and goes a long way towards preventing the operator from hanging himself.

I suspect the gasket in yours is worn out or MIA. It happens eventually.

All of the above notwithstanding, I don't imagine you'd have much success explaining to Kevin that nothing other than clean water should go into the reservoir and thus the heating chamber, and certainly not partially brewed coffee which will allow the water in it to boil up into the percolator tube and leave the increasingly scorched little coffee particles to burn against the heating element forever. Or at least in a very difficult to reach and clean place.

I'll leave you with my own coffee related anecdote, revolving around "Vic." Vic was our resident office coffee freak. And if I of all people am describing someone as being just a trifle too obsessed about coffee, you have a problem. If it wasn't directly work related, basically everything Vic talked about was coffee. "How's the coffee today? Has anyone refilled the coffee machine? Do you want some coffee? I'm going to go up front and get some coffee." Et friggin' cetera.

I'm ashamed to admit that this plan was not mine, but rather hatched by another coworker. He deliberately and meticulously (I believe scales were involved — this was after all a building full of engineers) began blending decaf into the office coffee machine over the course of a couple of months. Progressively, ultimately weaning Vic off of caffeine entirely. This was not only brilliant, but also completely diabolical. My metaphorical hat is off to him, even all these years later.

He kept the office running purely on decaf for a couple of weeks, and then one morning abruptly switched the entire shebang back to 100% regular coffee.

Vic spent the next couple of days living life on speed dial. Talking fast, walking fast, bouncing around all over the place and off the walls. He was like a squirrel on amphetamines. He absolutely did not notice. Everyone else did, though. It was hilarious.