It's My Job Apparently

Conversation at work this morning. M=Me, CW = Co-Worker

CW: Did you identify the $40.53 ACH?
M: (quizically) No, I'm not sure what you are talking about.
CW: Did you check the bank file?
M: No, what would I be looking for?
CW: For the items not identified.
M: OK, I can, but doesn't someone else identify those items?
CW: Well you should check before the end of the month to help.
M: OK, I can do that.
CW: Well, it's your job.
M: OK, but how was I supposed to know that?
CW: Well, it's your job.
M: OK, I will be glad to do that but how was I supposed to know that's my job?
CW: Well, it's your job.

I've been laughing all day. Since it's the first day of the month and we are really busy with two people out, another person kept saying to me "It's your job."