In my case, though my mother tried to be very careful until I was a teenager, I learned many words (such as "fuck" and "twat," two of my favorites to this day) from her. She sent me a link to an alien penis game the other day, and once thought it would be fun to send to me (at work, no less) a picture she'd taken at the zoo of a zebra with a hard-on, and in return I sent her a link to a dodge-the-dildo game, and a fun little flash game where you move a birth control pill around the screen trying to stop a horde of sperm. On the same line, squid sperm is a recurring joke between us after she watched a scientist masturbate a squid on The Learning Channel. (I told her to look up hentai online after she told me about this. I know she hasn't done it yet, because I'd have gotten an irate voice mail asking me what the fuck I was trying to do to her if she had.)
Contrary to the image that this presents, we both have a very strong sense of public propriety. We just don't see the need to be that reserved in private conversations. Most people I know are absolutely scandalized by this, and some people who don't know us well think we probably have an extremely dysfunctional relationship. We don't - neither of us would have it any other way. I'd much prefer this to a mother who refused to admit it when I became adult enough to discuss things like sex. So where are you with your parents? Would your parents be horrified if you dropped the f-bomb? Would it mortify you to hear your mother talk about penises?