I'm going to kick my roommate out after they pay rent next month
Why are you kicking him out?
They need to be out because their smell is disturbing me.
It is the right the to do to give notice when someone wants out of a living arrangement.  It is rude not to say something at all.
I don't have to give notice, I'm a friend, not their landlord. They will won't have any problems finding a new place to live. No one should live with people they hates.
If you are not their landlord, you should not be able to evict them. If you have the power to evict someone, you do need to give notice since it might be against the law to do it without notice.