Interesting to note that the phrase 'mutual friend' was originally considered very incorrect. And still is technically incorrect but people use it so much it doesn't seem to matter and it has taken on the meaning that people mistakenly thought it had, if that makes sense...
I studied Dickens' book 'Our Mutual Friend' at University and the title is a bit of a joke at a character in the book who uses that phrase which was considered at the time to be incorrect and a sign of someone trying to sound clever but showing their ignorance.
The phrase should of course be our common friend.
Here's Fowler on this phrase:
"Every one knows by now that our mutual friend is a solecism. Mutual implies an action or relation between two or more persons or things, A doing or standing to B as B does or stands to A. Let A and B be the persons indicated by our, C the friend. No such reciprocal relation is here implied between A and B (who for all we know may be enemies), but only a separate, though similar relation between each of them and C. There is no such thing as a mutual friend in the singular; but the phrase mutual friends may without nonsense be used to describe either A and C, B and C, or, if A and B happen to be also friends, A and B and C. Our mutual friend is nonsense; mutual friends, though not nonsense, is bad English, because it is tautological. It takes two to make a friendship, as to make a quarrel; and therefore all friends are mutual friends, and friends alone means as much as mutual friends. Mutual wellwishers on the other hand is good English as well as good sense, because it is possible for me to be a man's wellwisher though he hates me. Mutual love, understanding, insurance, benefits, dislike, mutual benefactors, backbiters, abettors, may all be correct, though they are also sometimes used incorrectly, like our mutual friend, where the right word would be common."
Sorry for being extra pedantic. I suspect that boycotting using this phrase is pointless.