This was the question my DS asked me the other day having watched the movie Avengers Assemble.
I didn't think anything of it and said "I've no idea darling, let's have a look on Google".
To my horror, I discovered that a mewling quim is a misogynistic way of describing a certain part of a lady's anatomy, luckily for me the particular website we looked at referred to it as a vagina as opposed to the other word that is used on other sites I have looked at since.
Now admittedly the film is actually rated 12 and my son is an unworldly 10 but naively I thought it was just a Marvel superhero film and therefore possibly rather violent but in a comic fantasy kind of way. I had no idea that film makers would consider using this kind of language between a male character and female character for a film with this rating.
My son then decided he needed more information on vaginas etc, so now it looks like the sex chat is on the agenda - something I was hoping to defer for a while.
I will never be able to think of Iron Man et al in the same way again!