Tilt your head back, open your mouth and hold your tongue down (opening the airway).
This is based on the fact that you never of anyone having the hiccups while sitting in a dentist chair. I thought it was nuts when I first heard it many years ago, but it worked then and it works now.
I used to drive a party bus (a mini-bus that shuttled college students to a local bar on the weekend evenings). The bus was empty until a guy and his girlfriend got on at a bar to go back to the campus. He had the hiccups and his girlfriend said that he'd had them all day and couldn't get rid of them. As a prank, I suggested the "dentist" trick and within seconds, he was cured. It shocked the heck out of me that it worked.
Since then, I found a job driving an expedited van delivering Caterpillar parts all over the country. Sometimes when I'd stop at a place and saw that the cashier had the hiccups, I told them to do the trick, then went back to get what I came in for. By the ime I got back, the hiccups were gone - this trick has *NEVER* failed.
You probably don't have the hiccups anymore by the time you read this, but keep it in mind for the next time. You will be surprised at how quick and effective it is.