I found this error on a Sherman Alexie poster in the hallway of the English department at my alma mater. Ironic, I know.
We have another case of pronoun/antecedent disagreement (on the text on the far right of the poster). The first word of the sentence is concealed, but the sentence reads, “Any man or woman with a book in their hand is sexier.”
The problem is that man and woman are singular, separated by the coordinating conjunction or, so the pronoun should not be their, a third-person plural pronoun. I don’t really like correcting these sorts of mistakes with his/her or he/she. The construction is rather awkward and interrupts the natural flow of a sentence.
To fix something like this, I like to, if at all possible, make the subject plural. In this case, that will work, so I would suggest this fix: “Men or women with books in their hands are sexier.”
People with books in their hands might be sexier, but those with books in their hands — and who use correct grammar — are sexiest.