The window displays at this Newbury Street boutique are sexy enough to make the most straitlaced Yankee blush. From sheer black chiffon nighties to exquisite embroidered lace-up corsets, the imported European lingerie here is welcome change from the mass-produced unmentionable found elsewhere. The staff is discreet but helpful, offering advice when asked and leaving shoppers to browse in peace when not. So what if the steep price tags can send the heart racing? So does the lingerie, which is why Belle de Jour is just as often filled with men sheepishly selecting lace peignoirs for their sweethearts as it is with women looking for embroidered bra and panty sets for themselves.