Modern utilitarism is more about minimizing suffering rather than maximizing happiness.
I'm not a full utilitarist anymore as I don't think a good utility function exist, but it is a good way to evaluate quickly if an action I do is more likely to do good than bad: 'do I risk hurting someone?'.
I think almost everyone is utilitarist, you probably are too. If one time you spent money to buy flowers or a gift for no reason but make someone happy, or you told a white lie/didn't tell the truth to avoid hurting someone, you're one too.
But like I said, it's not a good moral philosophy. It's useful in short burst, to take quick judgment on concrete, temporary actions, but it fails on larger ideas.
Which is fine tbh. I need philosophy to carry me through concrete decisions too, not just through political choices. Utilitarism is useful for the former, less for the later (in the best case you end up believing Pinker's statistics).
Preference(person, one_thing, other_thing) and it returns -1, 0 or 1 depending on what that person prefers?
You can do math on this and try to optimize it, it's just more complicated than if utility was cardinal and objective.
Someone might choose to maximise their personal happiness even knowing that their personal suffering would also increase (or even be maximised). Trite example: prisoner released from jail who sets out to kill the person who double-crossed him, knowing that he'll be re-incarcerated or even executed.
Happiness and suffering might be related but they're (somewhat) independent.
θ(-f(x))*(-f(x)) vs max(0, -f(x))