Ashton~
Your feet. As weird and odd as it sounds he loves your feet. They're smaller than his and you always have your toenails painted bright colors. He'll eye your feet when you're wearing any kind of open-toed shoes. Ashton loves your feet so much that he gives you foot massages.
Michael~
Your hair. Michael loves your hair, because it always smells good and soft. He'll run his fingers through your hair while smelling it. You have great hygiene especially with your hair. Michael loves it when you ask him to braid your hair or even brush it.
Luke~
Your hands. They're so much smaller than his, making him obsess over them. Your hands are also really soft and it provokes Luke to constantly hold them. Luke's so weird that he'll kiss your hands as well.
Calum~
Your boobs. As weird and very perverted as it sounds he loves them. When you two are laying down or cuddiling, Calum will use them as pillows and cuddle close to them. He even goes bra shopping with you, so your boobs look stylish.