Zozee, you just violated your own rule. "I'd rather give it to whomever won't waste it on donuts!" should be whoever. He won't waste it on donuts, therefore give it to whoever won't waste it on donuts.
That one is tricky, and I admit I had to look it up. The use of whomever/whoever is based on the dependent clause.
http://www.grammarbook.com/grammar/whoever.asp
I think more and more people are using whom when they should use who. And if those donuts are being passed around, you know who wants some. (Who = me, but in this case *I* want some.)