People don't know why they drive when they are drunk. When you are sober you think that you would not drive drunk. But when you are drunk, that's a different thing all together... You do stupid things when drunk.
Hiccups are usually caused by a lack of oxygen to the diaphragm. Hiccups are hard to get rid of once they start. Many people might get the hiccups just by eating a piece of bread without drinking water or another liquid.
It is not illegal to drive people who are drunk. In fact it is the best thing to do for a person who is drunk instead of letting the person drive his or her own vehicle while drunk. That is why "designated drivers" are important.