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1.
When you date or marry somebody in a similar line of work to your own, or even worse if it is with a colleague.
Person 1: did you hear that John is getting married?

Person 2: Really? I didn't even know he had a girlfriend!

Person 1: yeh he's been seeing Mary from HR for about 2 years!

Person 2: eugh, that's professional incest!
by borntoboogie October 19, 2010