The last time you wore a turtleneck was probably to conceal a hickey you got from the boy next door. Now you can get nostalgic as necklines on dresses, tops, and sweaters creep up for fall. But covering up doesn’t mean that sexiness levels have to go down. Short dresses, fitted tops, and form-fitting coats with high necks are also revealing in all the right ways. As always, Intermix (186 Newbury Street, Boston, 617.236.5172) delivers the goods on this season’s trend. Splurge on a Herve Leger sleeveless mock-neck Ombre dress for $1590, or opt for a more affordable floral wrap dress by Falls for $265.