Ex-Facebook employee spills social-network’s secrets in new book

"At one point in the tell-all, Losse says female employees were instructed to wear T-shirts with Zuckerberg’s face on them in honor of their wonderboy boss’ birthday. Male employees were told to wear Adidas sandals, she said, a nod to the CEO’s favorite footwear. To Losse, the order reeked of sexism and cult-like worship"

Is it just me or does this sound more like a funny prank than anything else?

Seems like a case of muckraking to me. I have several friends at Facebook and they all say that Facebook takes abuse very seriously. You can be disciplined (up to and including termination) for calling something gay, and similar. Perhaps at one point it was like this, but I seriously discount this as anything reflecting present culture.

And no, I don't work for Facebook.

I'm really skeptic, I can assume that unfortunately there was some sexual harassment but the stuff reported in the article/book seems too much. Where are the lawsuits?

This sounds very, very yellow. Probably just trying to score a lot of sales without much problem to exagerate/lie.