Luke: hasn't done anything special today. Used when talking about casual events. eg. "Luke is eating a banana on a toilet seat."
Luek: has done something silly. Often used as a synonym for the meme "moon moon". eg. "he just tripped over his own feet omg luek"
Lucas: has done/said something pg rated 18+. Something Liz would not be proud of. eg "put your pants back on, god lucas"
Lucifer: has done something slightly evil. synonym for Lucas but is often used before a swear word. eg. "Lucifer you fucking life ruiner"