I usually chip in with my solution for all generalized derogatory words for women: "ball sack." My 30 something friend substitutes in "scrotum," or "scrotums" when answering inappropriate cat calls. As in, "Hey, scrotums!" If nothing else, this calls the inappropriateness glaringly into the spotlight. I haven't come up with a non-gender-reliant term yet, but I am always alert to possibilities.
So, I try (not always successfully) to show my preferred wording, rather than correcting theirs. I restate. A big problem is that some women feminists use "bitch" and other women-putdowns, in order to contest them, or to reclaim them, as has been done with "crone." It is an uphill battle, but one that is worth waging, I think.
It seems like several of the replies in these comments implied that you were trying to defend your use of the offensive term, rather than trying to curtail its use by someone else. I'm trying to retrain myself to say, "I find that offensive," rather than "That is offensive (don't use it)." Also a hard climb.
edit: grammar, parenthetical