Don't argue with me

Some twat recently called to complain that I had fucked something up and, unfortunately, ended up talking to me on the phone.

Client: You guys screwed this up.  This is the second time it has happened and I'm going to be a HUGE bitch about it!
Me: I don't recall it happening the first time, but I'll go check and see what could have happened this time.
Client: You do that.
Me: It appears as though YOU sent us the wrong information.
Client: That couldn't be possible.
Me: Allow me to email you what you sent us.
Client: Oh.
Me: So, who screwed this up?
Client: It was a mutual mistake, really.
Me: Really?
Client: Well...
Me: Say it.
Client: ...
Me: Say it!
Client: I screwed it up.
Me: Thank you.

I really shouldn't be allowed to talk to clients.