I don't drink coffee, but I make it in quantity for a meeting once a month. Instead of dumping the leftovers, I give them to my 93 year old, completely with-it neighbor. She refrigerates it and keeps heating and drinking it until it's gone. She grew up in Alaska and wastes nothing. Because I know she does this, I've switched to cold brew coffee, which is laughably simple to make, and hopefully less bitter upon reheating.
I sometimes wonder if the go-out-for-coffee multiple times per day people aren't either 1. Smokers or 2. Reformed smokers. In the case of the former, "coffee" is the more acceptable break than "smoke". In the case of the latter, it gives them something to fiddle with instead of a cigarette. In those cases, one could argue that their coffee habit is saving them a ton of money over the exhorbitant cost of cigarettes, particularly if one considers the health costs of smoking.
Sidebar rant(s): k-cups are incredibly wasteful. Sure, you don't waste coffee, but you add so many tiny plastic cups to the landfill! Most commercially produced coffee cups are plastic lined and cannot be recycled. The volume of non-recyclable trash created by a single Starbucks per day is astronomical! Making your coffee at home or work is far more environmentally friendly, which is a nice bonus to the money you're saving.