"Everyone has lost their sanity."
This is bad English. "Everyone" is singular. It means "every person". That it is singular is evident from the meaning of "every" and "one", and also from the use of "has" instead of "have". "Their" therefore has no place here. What should have been said, therefore, is "his", i.e. "Everyone has lost his sanity." You can say "his or her", too, if you want: but that sounds silly (still less appealing to the ear would be "his/her").
This error has nothing to do with feminism, either. It is old. It is hundreds of years old. It is not an attempt to make our language "less sexist". It is a genuine error which is most unappealing to the ear.
This is bad English. "Everyone" is singular. It means "every person". That it is singular is evident from the meaning of "every" and "one", and also from the use of "has" instead of "have". "Their" therefore has no place here. What should have been said, therefore, is "his", i.e. "Everyone has lost his sanity." You can say "his or her", too, if you want: but that sounds silly (still less appealing to the ear would be "his/her").
This error has nothing to do with feminism, either. It is old. It is hundreds of years old. It is not an attempt to make our language "less sexist". It is a genuine error which is most unappealing to the ear.