Most people avoid using “whom” because they think it sounds, well, like you have a stick up your butt. There’s something prissy about it, something overly correct about it. But there is a time and place for whom, at least for purists. (Note: This is one case where we tend to side with the purists, although we concede that there is a lot of truth in that stick issue …)
When do you use whom and when do you use who? It’s really not tough. You use who as a subject, and whom as an object, indirect or direct. An indirect object use of whom goes like this: “To whom am I speaking to?” (“Who am I speaking to” is technically wrong, although we violate our own rule and say it ourselves.) A direct object use goes like this: “He hit whom?” Who works when you would use he, she, or they; whom with him, her, them. If you aren’t sure, just replace the who/whom with he or him. “Who/whom called me?” “He called me,” not “him called me.”
But avoiding “whom” is common nowadays. For example, a while back Infographic had a graphic: “Who had sex with who on Game of Thrones.” We don’t know the answer, but the question should have been “who had sex with whom” since “she had sex with he” is definitely wrong. Similarly, Twitter has a little box at the top of the screen saying “Who to follow.” You wouldn’t follow she, you’d follow her … so it should be “Whom.” Presumably Twitter is a little to casual for that correct “whom.”
Let us close with a particularly dreadful joke:
Knock knock.
Who’s there?
To.
To who?
It’s to whom!
We’d like to thank whoever (not whomever) actually laughed at that.