2 for the price of 1
Both work related.

1) Them: "You know, sarcasm is the lowest form of wit."
Me: "Yes, but Oscar Wilde was being sarcastic when he said it."

2) 'Her' is a colleague that was, when I joined, a little bit bitter that I could do a job in 1 month that she hadn't worked out in 6.
Her: "According to this file you haven't initialled this task to say you've done it."
Me: *Glance inside file* "That's because it hasn't been done."
Her: "Well why not..." *cue generic whining about time-limits and targets*
Me: *Looks more closely at the file* "Well if you'd read the task properly you'd notice that it was requested about 2 months before I even started working here." *Said loudly enough for the rest of the office to hear*

We didn't talk much after that, and I still only say hello to be polite.
(minister of heresy, Thu 29 Apr 2004, 16:13, Reply)