Designated Driver

At a party or other place that results in a lot of drinking on TV, especially if the place is far enough away to require driving, there is usually one person, pre-selected or out of his/her own volition, who has to not drink at all in order to remain sober enough to drive the other partygoers/drinkers home safely. This is known as the designated driver. This is a Truth in Television, as most times in order to follow road safety laws, people aren't allowed to drive home if drunk.

Examples:

Live Action TV

 * Inverted on the Monk episode Mr. Monk Is the Best Man. Because Stottlemeyer let Monk plan his bachelor's party, Monk supplied 12-ounce bottles of beer to each of the 12 members, resulting in 144 ounces total. In Stottlemeyer's words, that meant they only had enough to make them just slightly sleepy (i.e.,, not drunk enough to require designated driving), or to give it all to one of the members to make him very polluted and make him the Designated Drunk. The majority of the partygoers ultimately go with the latter decision, and Randy Disher volunteers to become the "designated drunk".

Western Animation

 * In The Simpsons episode "New York City vs. Homer Simpson", Moe's Tavern ends up having to institute a new designated drivers policy after his patron's drunken antics caused a lot of car accidents. Because of this, Moe supplies each patron with a pickled egg from his jar, and the one who got the black pickled egg has to be the designated driver for the night. Barney ended up getting said black egg, thus forcing the Town Drunk to go sober for the night, causing hilarity to ensue when his attempts to avoid drinking become even more difficult when Duffman and his cheerleading squad arrive at Moe's Tavern to hold a party in Barney's honor after winning a contest.
 * Subverted in an earlier episode, "Homer vs the 18th Amendment", where Moe tells all of the arriving patrons that it is going to be the biggest drinking day of the year due to it being St. Patrick's Day, and asks for the Designated Drivers to identify themselves. He then tells them, "Beat it. I have no time for cheapskates."