Loco-foco: member of a radical faction of the Democratic party in the 1830s; later, a disparaging nickname for all Democrats
Loco-foco (sometimes spelled locofoco) started out as a name for a patented self-lighting match introduced in the early 1830s. Loco-foco cigars, with a self-lighting contraption on the end, were a popular novelty item in New York City for a time. According to J. D. Hammond's Political History of New York, the name was transferred to the Democrats after a memorable 1835 Party meeting to organize the state's Democratic congressional campaign.
New York Dems at that time were divided into two opposing groups. On one side were staunch supporters of Tammany Hall, the long-time Democratic machine in New York. On the other side were members of a radical reforming faction who supported President Andrew Jackson's attempts to weaken the national bank. They were in favor of gold and silver currency rather than paper money. They also believed in labor unions and equal rights for all. In 1836 they would form their own Equal Rights Party.
As Hammond describes it both factions, eager to take control of the nominating meeting, congregated outside the Hall well ahead of time. As soon as the doors opened, Equal Righters burst through the front door and rushed up the stairs to the meeting room, while the Tammanies charged up the back stairs. What Hammond calls "a very tumultuous and confused scene" ensued, during which the gas lamps that lit the room were extinguished. Apparently the radicals had been warned ahead of time that their opponents might use this ploy to break up the meeting. They had come prepared with the self-igniting Loco-Foco matches and a supply of candles. These they proceeded to light up and the nominating process continued. In spite of their efforts the regular Tammany slate triumphed in the end.
When newspapers heard about the evening's rumpus, they immediately dubbed the Equal Righters Loco-Focos. The Whig Party then started using Loco-Foco as a derogatory nickname for the entire Democratic Party, implying that all Democrats were "loco," or crazy. (The name of the matches probably comes from the Spanish words for crazy and fire—loco and fuego.)
Enemies of the Equal Rights Party gave them other nicknames as well. Epithets printed in the New York Times include several names that allude to the match-lighting episode—Fireflies of Faction, Jack o' Lanterns who shine in an unhealthy atmosphere, Small Lights, and the Guy Fawkeses of Politics—as well as several general insults—Disorganizers, Intruders, Rowdies, Pests of Party, and Infidels.
For more about New York's rowdy political scene of the 1830s and 1840s, see Barnburner and Old Hunker.