Doing it old school.

Co-worker- "By the time I was 16, I was totally bored with school."
Me- "I suppose you knew it all by then."

No one likes a smuggie.

Dear Co-worker,

All the smug looks, asides and hints are becoming really tiresome.

If you want to tell me you've applied for another job, just come out with it.

Paging Victoria Coren Mitchell

Dear Co-worker,

Please stop demanding my attention.

This Only Connect wall is against the clock you know!

Not wanted on voyage?

Dear Co-worker,

Yes, I agree that stag dos are getting a bit out of hand when you have to go to New York or Thailand for a week.

But don't worry. It's very unlikely you'll ever be invited on one.