Jimmy and Scott grew up in the same Brooklyn neighborhood. Although he was a year and a half younger, Jimmy entered show business first, in Joe and Sons (1975-76), a short-lived sitcom about an Italian-American family.
While Scott was playing a preteen gangster with a lascivious girlfriend in Bugsy Malone (1976), Jimmy was buddy-bonding. In The Bad News Bears in Breaking Training (1977), former Little League superstar Kelly Leak (Jackie Earle Haley) decides to rejoin the team and reconcile with his father, the coach. He brings a friend from New York, Carmen Ronzonni (Jimmy), who is called both racist and anti-gay slurs by his belligerent teammates, marking the pubescent relationship as potentially gay. To assuage them, Carmen buys some Playboy magazines to pass around, but significantly doesn't read them himself.
In the fall of 1977, both cousins landed tv series. Scott was brought aboard Happy Days, to draw a teen demographic to the rapidly aging cast.
Jimmy leaped head-first into a firestorm of controversy on the soap opera spoof Soap. Even before the first episode aired, it was receiving vociferous protests from religious groups, gay rights activists, tv watchdogs, and even the National Football League.
People calmed down a little (not much) when they discovered that the program was simply a parodic exaggeration of the themes soap operas had been displaying for years, usually involving falling in love with the "wrong" person:
Your tennis coach (when you are married to someone else)
Your priest
The escaped convict who is holding you hostage
A woman (when you are gay)
Someone of another race
Billy's job was to be kind, understanding, and "normal," a stable observer of the lunacy around him. Significantly, he was the first teenage character on tv (and the only one for many years thereafter) to treat gayness as perfectly ordinary, not bizarre or gross/disgusting. His interaction with his cousin Jodie (Billy Crystal), who veered between gay, transgendered, and bisexual, is a model of nonchalance.
Stable observers don't get many plot arcs of their own, and Billy only got two: he was kidnapped and brainwashed by a religious cult (a common fear of the period), and he was seduced by his teacher -- his only heterosexual relationship during the series. After their breakup, she tried to kill him several times, in wacky and ineffectual ways.
When the teen magazines came calling, Jimmy allowed some shirtless shots, revealing a lean, smooth chest and surprisingly firm biceps, but being presented as an object of desire to millions of teenagers made him feel insecure and manipulated.
He refused swimsuit and speedo shots altogether. Usually he insisted on wearing clothes, and let a friend handle the beefcake (in this case, Timothy Van Patten).
His gay fans didn't mind the lack of nudity; his dreamy smile -- and the assurance that he thought they were ok -- was enough.
When Soap ended in 1981, Jimmy continued to play teenagers for several years, in The Facts of Life, Matt Houston, and Trapper John, MD. But he was disillusioned with Hollywood, and his roles became sporadic. Most recently, in 2008, he appeared in the Godfather parody Don Justice.
Today Jimmy lives in New York City, where he has happily left stardom behind. According to rumor, he doesn't get along with his conservative cousin Scott.