Lucifer: Whenever you notice he didn't get a lot of sleep, you would take him outside and he would lay down on your lap and fall asleep.
Mammon: He would get very flustered when doing so. You'd tease him too. " Be grateful that the Great Y/N has allowed you to lay down on their lap." You would say.
Levi: he would do it whenever he lost a game. " Just let me lay here for a while okay?" He would say.
Satan: He would do it whenever you two are reading together. He thinks your lap is more comfortable than any pillow when reading.
Asmo: He would always do it after sex. " Your lap is so warm. Maybe I'll fall asleep." He would say.
Beel: When he felt lonely, he would do it. " Can I just lay here for a while? Please?" He would ask.
Belphie: He would do it when you guys sleep together in the attic. He would choose you over a pillow anytime.
Diavolo: He would do it whenever he's alone with you. Since he's always surrounded by tons of people and has countless things to do as the prince of the Devildom, he doesn't get to see you too much outside of school. So whenever he has some alone time with you, he'll lay down on your lap and take in your warmth.
Barbatos: He would do it after a long day of work. Even an amazing butler like him needs to unwind sometimes.
Simeon: He would do it whenever he feels like it. When you're alone in a classroom? Sure. When you're sitting outside? Why not. In the Purgatory Hall common room? Count him in. If he sees an opening, he'll take it.
Luke: He would do it whenever he's sad or tired. You would let him stay there for as long as he wanted to and just stroke his hair.
Solomon: He would do it where ever he wants in public places. He wouldn't care who saw you two. He also loved how you got flustered whee he did it in public.
Mephistopheles: He would do it when he's stressed about writing his articles. Whenever he gets writer's block, he'd go over to you and lay down on your lap. Once he had inspiration again, he'd get right back to work. Only to come back over to you a couple of minutes later.
Raphael: Same as Simeon.
Thirteen: She'd do it after a fight with her sister. She would always be very emotional and apparently laying down on your lap helps.