Recently, NBC's ''Today'' show reported a new trend among teenagers - no coats.  Now we're not talking about no coats when it's warm. Or no sports coats when going out on the town. Apparently, a lot of teenagers are not wearing their winter coats in the middle of the winter. And they are claiming they are not cold!  Average Josephine can understand a fashion rebellion as much as the next girl - she did, after all, jump head-first into the acid wash fad of the 1980s - but this trend isn't just silly, it's also chilly (excuse the pun). Who wants to be goose-bumpy and cold all the time? Not to mention all the stylish coats out there to choose from.  A hip-length pea coat is one of Average Josephine's favorite looks. It says, ''I'm hip,'' ''I'm fashionable'' and ''I'm smart enough to wear a coat when it's cold.'' Puffy coats are also really hot this year. Although those sold in the juniors section may be a little short in the eyes of a grown woman, you can also find knee-length puffy coats with faux fur hoods that are sophisticated and cozy.  Average Josephine usually bums around town in a merino wool knee-length pink trench coat that is both winter-appropriate and stylish.  So with all these choices, why are young people turning their backs on a staple of the American wardrobe?  National Public Radio reports that kids give a number of reasons for giving up winter coats, including being uncomfortable. Teenagers also point to other kids who wear even more inappropriate clothes and shoes in the winter, such as flip-flops.  Average Josephine thinks it's just teenagers being teenagers. Twenty years from now when another Average Josephine has taken over this column, she will write about her goofy teen years, too. Instead of acid wash, there will be ''no coats.'' Instead of stirrup pants with pointy-toed granny boots, there will be flip-flops in the winter. And instead of pleated baggy jeans, there will be low-riders that expose parts usually only shown by plumbers.  Until then, Average Josephine will try to be the voice of reason here. Young ladies, you need to go back inside your house right now and put on your winter coat. It may be wise to add a hat, scarf and gloves. Boots are also a good idea.  You'll thank Average Josephine when you're older.