Funny, no one ever says anything like that when I roll around with my granddaughters, and I often call for "girl power" as I take my feet off the pedals and make them power us. I guess it's okay to disrespect women, but not little girls.
Actually, I think people really want to say something nice and witty, but just can't think of anything in the short time available during a typical bike encounter. When we get the "not pedaling comment, usually directed at the stoker (me, the male), we just chuckle and I tell them to shush so she won't find out. If their intent is positive, I refuse to read negativity into it even when their words reveal something that could be interpreted thus. It's probably harder for women, who get hit with this disrespect constantly, to let it go.