Can I tell you that I had a big mess to clean up but I blew it off?
Really? Why didn't you clean up a mess?
I had better things to do.
What you did is irresponsible,  you should clean up the mess you made.
Why should I clean up after my cat if he makes a big mess? The cat did it, not me.
It is your responsibility since it is your cat. That is what you sign up for when you care for an animal.