I had it from a reliable source--corroborated by Snopes in the spirit of trust-but-verify--that the legend of Van Halen's M & Ms was actually not a matter of rock star vanity, but, rather, a mechanism to keep them and their roadies from injury and possible death.
Now, I'm not at all positive that I will ever have anyone at all working for me, much less enough people to make bringing in a box of donuts anything but overkill. But if somehow that happens, I'm seriously leaning toward inserting a clause in the employment contract to the effect that leaving part of a donut in the box is grounds for termination.
True, it's partly a matter of the fact that this is a huge peeve of mine. And it's equally true that I harbor a dictatorial streak left over from being the defacto babysitter of my younger sister. You'll have no quibble with me on either score. But kindly keep your sprinkles on long enough for the rationale.
Similar to Van Halen's thinking, such a clause serves as a very detectable indication that the employment contract was not read--or at least not taken seriously--by the employee. As a reading-and-comprehension test, it's pretty darned cheap, even when you pick up something considerably better than the grease-sponges at the gas station on your way in to the office. And I think that anyone who's played hiring roulette can agree that it's better for all involved to show your mistakes the door sooner than later.
Please understand that I've lived in the upper Midwest all my life. Here, we tend to say "Please" and "Thank you" and stand in line patiently, try not to be a bother and all that. Trust me, I get it: It's in my DNA, fer' cryin' out loud. But the half-donut thing is not part of that ethos. Bisecting a donut, leaving it to dry out and (if applicable) hemorrhage its filling basically tells your co-workers that they can have your seconds, because their enjoyment of the treat takes a back seat to your delusions of not getting fat.
Now, if you and a co-worker agree to split the donut, wonderful. That's win-win, and I like to encourage that. Or if, after a bite, you decide that it's too greasy or otherwise objectionable, tell me straight-up and pitch it into my trashcan. That's decision-making and honesty, and I like to encourage that as well. But anything else is symtomatic of a self-involved and self-delusional personality, and I won't foist that on the people whose work pays the bills. Either eat the d--ned thing and take the consequences to the Stairmaster or show some restraint and stick with your coffee.