I've seen NTs catch each other with the straight-faced joke, too. It's not just us. I just laugh and blow it off when I found out I've been "had".
If the same person does it a lot, I take everything he/she says as a joke until I know different. Most people do, in that situation. If a boss says the joker complained, I just tell them that no one can tell when whosit is joking or not. My co-workers have always backed me up on that.
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To eliminate poverty, you have to eliminate at least three things: time, the bell curve and the Pauli Exclusion Principle. Have fun.