During the time when the Ares 3 crew has direct video contact with Earth, Johansen has a uncomfortable conversation with her father in which she implies that Commander Lewis had told her that in the case of the supply mission failing, the rest of the crew would commit suicide so Johansen could survive (presumably by cannibalism).
Later, during the preparation to receive the supplies, Martinez jokes to Johansen about who she would eat first, saying things about himself tasting the best and remarking "I thought you liked Mexican."
When I first read the book, I thought it was a deliberate joke on Johansen and the reader, as one gets very somber while hearing the conversation with her father, but then the reader is surprised to hear Martinez joke about it like nothing. I assumed that it was because the crew was playing a trick on Johansen to make her feel uncomfortable for being the "chosen one" and make her squeamish. It also fits the structure of the rest of the book where Watney will think one thing and the next chapter be surprised at the outcome.
However, when I was listening to Still Untitled: The Adam Savage Project's spoilercast of the book, they seemed to act like the plan for cannibalism was a serious one, with one host Norm remarking "at least that's only in there for one chapter"
Which one is it? Are they seriously considering suicide and cannibalism, or were they just trolling Johansen?