Michael: "Food stealer" He insisted on putting that once you would steal bits of his food when you two were out anywhere and always calls you a food stealer.
Ashton: "Cutie Patootie" Ashton either calls you cutie or cutie patootie because he knows how much it makes you blush and he loves making you blush.
Calum: "Sugar Plum" You once called him sugar plum and he loved it too much so it became your new nickname.
Luke: "(Y/N) ❤" He had 'The original slim slady' as your name but you stole it and put that as his name so he went original and just had your name.
