Javier Andrade is holding an armful of shirts that are, for lack of a better word, pretty. There are two with ruffles, one bibbed with baby blue pleats, another in denim with rows of fuzzy and frayed pin-tucking and a swashbuckle creation with layers and layers of frilly fabric.

Shirts along the line you’ve seen on prom night or at the opera — or on your sister. But Andrade, a 30-year-old law firm accountant, is not shopping for herself or for any tuxedo-expected event. He’s buying them to wear with jeans.

The relaxed tuxedo shirt is tweaking a lot of old ideas about what a guy should be caught wearing. It’s a way to make the informal a bit formal, add some frills to a men’s garment that’s expected to be no-frills. The shirt is typically worn open at the neck, unstarched (almost as if it were just pulled out of the dryer) and not tucked in. What the shirt isn’t really meant to be worn with is a tux — unless it’s low-rise, boot-cut and looks like it’s been tortured to death.

“Right now, there are more tuxedo shirts available than I’ve ever seen before, and they’re coming from designers and manufacturers that aren’t specialists in tuxedo shirts,” says David Wolfe of Doneger Group, a New York-based company that analyzes fashion trends. “That’s a clue to a wider-spread trend for men that really comes from the urge to dress up and not be sloppy but also not be formal.”

And did we say sexy?

“It’s sexy dressing, for sure, and fun because the look is very rock ‘n’ roll, like L.A.,” says Sara Dovan, the owner of Traffic, a haberdashery at L.A.’s Beverly Center that has been doing brisk business with tux shirts by Comme des Garcons, New York Industrie, Romeo Gigli and Fujiwara. “The best thing is that you don’t need an excuse like a black-tie invitation to wear one. Just add blue jeans and a guitar.”

No guitars, but big-shot designers Ralph Lauren and Karl Lagerfeld were wearing tux shirts and jeans at their recent New York and Paris runway shows; John Varvatos sported a lavender ruffled shirt, faded jeans and smoking jacket at a benefit this month at his Melrose Avenue shop.

“The business of fashion is always looking for new ways to take something that has been around and re-invent it,” says Marshal Cohen, co-president of NPDFashionworld.