Where did the 'cops eat doughnuts' cliche come from? And other weird things

[SpiderClops]

That's a weirdly specific cliche.

[Caivu]

From the page about this trope:

In actuality, the association between police officers and donuts is less insulting and more practical. Cops will usually consume lots of coffee, because it's necessary for them to stay awake during the night, and the donut pairs well as a sweet to dunk in coffee or to remove its bitter aftertaste — all of which Makes Sense In Context. Donuts are also ready-made, boxed for easy storage, and do not melt or get inedible when old (depending on the recipe, some may only be edible for a few hours). They also tend to be both filling and cheap, and as donut shops tend to open early, for a while they were among the few places open for someone working the graveyard shift. Donut shops also tend to give out free donuts to law enforcement, partly as a public service and partly to encourage cops to hang around (and robbers to stay away).

[Grapeweasel]

It came from studying the fossilized remains of Neanderthal cops.