I don't want to allow students to come in late to my class
Is there a policy in your school against coming in late?
Yes, we have a proper policy on this. I'm just mean and nasty to them as I don't care about my students as they are
It is good to follow the rules but you should be a bit lenient with the time frame. If they are chronically late you should be able to remove them from your class.
I don't give a shit. I hate my students and I'm going to be mean right to their faces.
Teachers should care about their students, not be mean to them. If they've got a reason for always coming in late, try talking to them politely after class and finding out why. If you have to remove them from the class, do so without insulting them. Remember, you're the professional in this situation.