Julius Hart, 17, was charged last week after an officer said he spotted the teenager riding his bicycle with 4 inches to 5 inches of blue-and-black boxer shorts revealed.
Hart's public defender, Carol Bickerstaff, urged a judge Monday to strike down the sagging pants law, telling him: "Your honor, we now have the fashion police."
Circuit Judge Paul Moyle ruled that the law was unconstitutional based on "the limited facts" of the case. Technically, however, the charge hasn't been dropped yet: a new arraignment awaits Hart on Oct. 5.
Voters in Riviera Beach approved the law in March. A first offense for sagging pants carries a $150 fine or community service, and habitual offenders face the possibility of jail time.
Proposals to ban saggy pants are gaining ground in several places around the U.S., and have met with opposition from civil liberties advocates who say they will lead to racial profiling against young African-Americans.
The fashion is believed to have started in prisons, where inmates are not given belts with their baggy uniform pants to prevent hangings and beatings. By the late 1980s, the trend had made it to gangster rap videos, then went on to skateboarders in the suburbs and high school hallways.
Bickerstaff said she wants the city to drop the law - regardless of whether anyone dislikes low-riding pants.
"The first time I saw this particular fashion, I disliked it," she told the judge. "And then I realized I'm getting old."
The issue in Riviera Beach illustrates a larger trend among U.S. cities that have outlawed the fashion trend.
For example, in Flint, Mich., a city with a similar law banning droopy drawers, Police Chief David Dicks said his officers will continue to arrest violators in spite of the Florida ruling. Dicks called the style of dress "disorderly" in an interview with The Detroit Free Press.
And the hubbub isn't isolated to suburban areas either. Last year, in Dallas, Deputy Mayor Pro Tem Dwaine Caraway proposed that the city council send a message to young men in his city; Pull your pants up.
"This is not about the government trying to control how you dress," Mr. Caraway told The Dallas Morning News. "It's to protect the rights of others who don't want to see someone's butt."