1 Co-Pilot: {over the cabin PA system} Ladies and gentlemen, this is your co-pilot. If there is a herpetologist on board, please identify yourself to the crew.
2 Terry: I wonder what that could be about?
2 Steve: No idea.
3 Terry: You should put your hand up, Steve. You're probably the closest thing to a herpetologist on board.
4 Steve: But crikey, Terry! I don't know anything about medicine!

A suggested version of the final panel, thanks to a commenter who shall remain nameless:

Steve: But crikey, Terry! You know I don't have...
Terry: A herpetologist is someone who studies reptiles, Steve.

This was getting a little too close to the PG rating line for my comfort.

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2018-04-07 Rerun commentary: I wonder what the strangest occupation that has ever been called for by a flight crew in need of assistance is.

When booking flights, I used to put "Dr" as my title on the booking, since as a Ph.D. I am entitled to use that title and I've always thought it's cool. Until one time a flight attendant came up to my seat and asked me if I could help a passenger who had fallen ill. I had to explain that I wasn't a medical doctor. Although in hindsight, maybe it would have been interesting to fake it...

Anyway, ever since then, I just put plain old "Mr" on my flight bookings.