In the 10 Jan 1997 article “What are hiccups and why do we get them?” (pls forgive me - I don’t know how to link yet), Cecil reported on a numerous amount of proposed solutions to a case of the hiccups.
I remember (or, more accurately, half-remember from a long-ago and half-forgotten source) hearing that hiccups are like a “mistake” in the way your body processes oxygen (on the chemical level, of course - it’s hard to make a mistake in the mechanics of breathing).
Thus, I have found a solution that works, at least for me, every time.
It’s holding your breath. The trick, however, is to hold your breath until you’re nearly ready to pass out; until real panic begins to set in. This (I think) depletes enough of the oxygen from the chemical pathways that it will “reset” your oxygen pathways and break you out of the self-reinforcing cycle of hiccups.
Unfortunately, depriving yourself of oxygen like this probably kills brain cells. But isn’t the loss of consciousness supposed to protect your brain from a lack of oxygen? And you’re not depriving yourself of oxygen enough to trigger a loss of consciousness, anyway, right?