I'm going to kick my roommate out.
Why do you want to kick your roommate out?
Their cat is shitting everywhere, and they aren't doing anything about it.
I completely understand why you are upset at your roommate for their cat's behavior. You should talk to your roommate and explain how you are feeling and tell them that they need to take more responsibility for their pet. If they refuse to do so, then it's fine to ask them to move out.
I already did. I got two alcoholic drunks to move in with me to replace them.
I'm glad to hear that you found a replacement for the previous bad roommate. I hope your new roommates are more respectful!