a teaspoon of vinegar.
despite the nonsense talk about trapped nerves and whatever hiccups are in fact an involuntary spasm of the diaphragm. the acidity of the vinegar stops the spasms.
"A hiccup or hiccough (pronounced /ˈhɪkəp/ hik-əp) is a contraction of the diaphragm that repeats several times per minute."
"Vinegar may stimulate the dorsal wall of the nasopharynx, where the pharyngeal branch of the glossopharyngeal nerve (the afferent of the hiccup reflex arc) is located."
http://en.wikipedia.org/wiki/Hiccup#Treatment