Mentally distract the hiccupee for at least one minute. For instance; ask him/her what they meant yesterday at lunch when they mentioned ..?..?..?. While they are thinking what they may have said, it seems they forget about the hiccups.
I usually breathe in as deeply as I can, and then breathe out until there's no more to come out, and I do that several times. That generally cures me! :-)
Breathe into a paper bag. This is supposed to increase the carbon dioxide level that you are breathing, which makes the medulla oblongata alter the depth of breathing. (Or that's what they say in first aid!) Amazingly, this is the only way that I've tried that definitely does work.
I find holding my breath for a minute or so always does it, but you need to exercise great diaphragm control to stop the hiccups from happening. Sometimes i find curling up in a ball on a bed or sofa hugging my knees to my chest helps, whilst holding my breath. Tip: Don't forget to start breathing again.
Diaphragm control is the best method as it does not required anything difficult or make you look like a wally in public. One cure which has always worked for me is to drink a spoonful of vinegar - instant cure and it even works on sceptics!
I have got a cure for hiccups that has never failed yet, but you will have to email me on [email protected] if you want to know what it is. It was passed down to me by my dad, and I feel somewhat protective towards it.