The nipple fruit is something you'll see gracing many Lunar New Year flower displays, rather than your plate. The waxy, bright yellow fruit - whose protuberances resemble mammary glands - is a common sight at this time of year. It's considered an auspicious thing to have in the house around this time, especially if the fruit has five "nipples", which represent five generations of a family living under one roof (yes, some people think that's a good thing). The fruit grows on long branches that have sharp spikes, which are trimmed off before the fruit is sold in flower markets. When buying them, look for glossy specimens; if they're dull and matte, the fruit is old and will soon start to shrivel.
Don't try eating this fruit: most of the reports I've read say it's poisonous, while others say unripe fruit can be cooked and eaten (but I wouldn't advise it). A member of the nightshade family - it's related to the eggplant and tomato - the fruit is under research as a potential treatment for some cancers. It's also said to work as a detergent for washing clothes.