sexist, sexiest

Sexist or sexist describes the behavior or attitude of someone who believes that women are inferior to men--
He's very sexist; he thinks all women should stay barefoot and pregnant.
She knows he's sexist, but she thinks he'll change.

Sexiest or sexiest describes a person, thing, or idea that garners the most sexual or romantic interest or attraction--
They are watching a competition to find the sexiest person on TV.
That is the sexiest car commercial I have ever seen.

Now that you know that, you can say--
"She thinks the book is sexist; he thinks it's the sexiest thing he's read in a long time."