It may have started with men and women wearing tuxedo shirts from second-hand stores for informal occasions. Or maybe the supersized tuxedo shirt Kenzo showed last year in Paris kicked off the craze.

Whatever the reason, tuxedo shirts, often with pleated fronts, are showing up for spring as nightshirts, tops for skirts and pants, even lingerie. (The only people wearing them less are those in black tie, many of whom are subbing plain styles for the formal shirt.)

From left to right: White tuxedo front shirt dress by Serbin Fashions has black bow tie and belt, from Saks Fifth Avenue. Tuxedo teddy is worn with tap pants, both from Sheer Madness at Woodward & Lothrop (later). Vintage tuxedo shirt worn with shorts, from Commander Salamander. Kenedy's supersized tuxedo shirt from his collection for spring.

Men used to stand on tree tops with tiny bows and arrows to shoot butterflies for royalty, but now they've landed just about everywhere - in jewelry, fabrics for fashions and home furnishings and stationery. Even on postage stamps the butterfly is difficult to catch - the colorful block of four butterfly 13-cent stamps introduced last June sold out quickly from most post offices and was voted the most popular stamp of 1977 by Linn's Stamp News readers. In London they've been wearing enamel butterfly pins to decorate jacket lapels and an exhibition at the Commonwealth Institute there centering on the butterfly opened recently. It includes not only butterfly-inspired art, from Japanese batik to Aubrey Beardsley drawings, but commercial uses and a film by Cambridge University zoologists.

People like butterflies because they're pretty, never fade and are thought of in terms of "freedom, lightheartedness and happiness" says Sarah Reinhardt, one of the owners of Butterflies, Ltd., which sells, among other things, butterflies in Plexiglas furniture. Increased demand has driven butterfly prices up 30 percent since last summer, says Reinhardt. Most butterflies used commercially are raised on farms, with a natural lifespan of three to four days. They are picked from the ground when they die. (There are Chinese enamel butterflies as earrings at Full Circle in Alexandria, porcelain napkin rings at Bailey Banks and Biddle.)

What's after butterflies? David Berkowitz of Sakowitz in Houston, placing his order at Fiorucci in Milan, predicts strawberries. Pointing to the strawberry Fiorucci accessories, Berkowitz says, "It is so erotic, so red." Says Elio Fiorucci, "Well, that never occurred to me, I think it is a nice fruit. That is all."

Meanwhile, after their big success with the butterfly stamp, the folks at the post offcie will be issuing a block of four owl stamps later this year.

Bad Taste Award of the Week: the cover photo of Women's Wear Daily Thursday placing the model clad in black in a cemetery setting. "Drop Dead Fashion" is the headline and the copy reads, "It's to die over. It's divine. The fall frockcoat dress according to Stan Herman. . .

Helga Orfilla was wearing three coats of two colors to the party honoring syndicated fashion columnist Eugenia Sheppard and Earl Blackwell, celebrity publicist, earlier this week. She says she sometimes even wears four at once, alternating layers of red and black. They are unlined silk and at the Sheppard party she wore them over a strapless top and tapered rumpled pants, all by Zoran. According to husband Alejandro, secretary general of the OAS, there are lots of additional parts that "can be mixed up." Helga Orfila adds that the new pants may look fine, but are difficult to wear because they tend to slip down over the heel and catch in shoes.

Sheppard and Blackwell were in town for a book-signing session at Woodies for their novel "Crystal Clear."

Estee Lauder has taken the principle of layering, as in building makeup from a moisturizer and foundation or layering clothes, and applied it to fragrances. She's about to introduce three varied frangrances and suggests not putting atop the other (lest you lose the individuality of each), but wearing them side by side or "layering vertically" - a different one on the shoulder, the wrist and the back of the knees.Another possibility is spraying on a different one of the three scents, called White Linen, Celadon and Pavilion, as the day wears on. "It cuts out the risk of nose fatigue," says Lauder, referring to the numbness to one scent one gets from using the same fragrance all the time. Lauder also recommends wearing two different lipstick colors at one time to create a unique shade for the wearer.

Three-legged pantyhose? Actually it's not such a dumb idea if you consider it in the spare tire principle. The most exasperating thing about pantyhose is having to discard a pair with a rip in one leg. So Tria and Take Three are test-marketing individual leg pantyhose, each leg crotchless and with a waistband so that the ripped one can be replaced.

Stymied by what to do with an old dance program, grandfather's collar hook or calling card case? Lynne Loube has tipped them in gold and hung them from gold or silver chains as part of her collection of sculpture to wear at Harriet Kassman.

Too late for this year, but, for plan ahead types, Kar Ben Copies has come up with a T-shirt for the child who finds the Afikomen, the hidden matzohat the Passover seder. It has "I found it" in print and the picture of half a matzoh. It's the creation of Judye Saypol and Madeline Wikler for their Silver Spring firm, Kaar Ben (593-2563).