It's odd - I don't see defining a utility function for myself as especially hard. Looking at it dispassionately, I want food, access to new information, ability to make my own decisions, shelter, sex (in roughly that order of importance, with food at the top) up to the maximum levels I can comfortably cope with those things, and as much assurance as possible that I can continue to get those things. I want to continue to be supplied those things indefinitely, and to avoid pain. I also want to see as many other utility functions fulfilled as possible - but where a conflict comes up between two different utility functions, I would give preferential treatment to the utility functions of beings who are cognitively closer to me than to those further away.

This means that all else being equal, I would rather see everyone get maximum utilons, but if it's a choice between satisfying the utility function of a liberal music-loving science fiction fan or that of a conservative religious fundamentalist who wants to ban all non-worship music, I'd choose the former over the latter. But I'd choose the religious fundamentalist over a monkey, a monkey over a dog, a dog over a slug, and a slug over a lump of rock. And were there a way to make the rock happier (should such a concept even make sense) without disadvantaging any of the things higher in the list, I'd want to see that happen too.

I also have a few people whose happiness I rate at least as highly as mine (my wife and my parents are the only ones who wouldn't necessarily be covered by the 'cognitively similar' part) and so my own utility function would give 'undue' weight to them, but oherwise seems fairly simple.