okay, another question. how do Mark and Mary know when your group is planning to get together? do you use some kind of social networking site? is that how Mary can pop up and say "oh no, don't go somewhere and have fun, come cram yourselves into my living room like sardines and whisper for a few hours"? 
A lot of the planning is done over facebook. We have a group set up especially for those involved in our group where we can post events and talk about plans which is a lot easier to do than having to call up each person and trying to track who can do what. They have access to the group and can see whatever is being discuses. We'll also sometimes just text each other with plans if we don't want to use facebook.
Regarding the two bolded sections. Many people learn to drink, swear and tell dirty jokes from their peers later in life and hide these abilities from their parents pretty well.
It's not an unusual stance for parents to try to cut out their own swearing around their young kids. Even if they feel fine with adults swearing, they may feel like a stream of Fs coming out of a toddler's mouth is a little off.
I have to agree with CakeEater.on this. I learned to drink, swear and tell dirty jokes from my peers late in my high school and in my university years mostly. These aren't things I learned from my parents and most of us go out of our way to be on our best behavior in front of our parents. Just because they don't want us swearing around Junior wouldn't make me think that there is anything wrong with them. They're just overprotective (in my opinion) not psychologically defective.
Anyway, there has been an update and it's a real doozy. Please note that a lot of what happened between Mary and Claire is second-hand information so take it with a grain of salt.
UPDATEOn our facebook group, Claire posted about all of us going to a piano bar this Saturday since her cousin was performing and we could get a nice group discount on drinks and food. The plan was to meet at her and Clark's place first at around 8 pm and then we could all head over to the piano bar since it was only a couple of blocks away from their apartment. Everyone was looking forward to it and accepted the invitation talking about how they couldn't wait until Mary chimed in with this little gem: (This conversation was on the fb wall of our group)
Mary's Post: Gee, it must be nice that you guys can go out and get drunk while the rest of us have responsibilities to deal with.
Claire: Sure is! I love going out and being all irresponsible and not trying to push my choices on other people.
Mary: Funny. Nice to know who our real friends are. Real friends wouldn't keep scheduling stuff when they know we can't come.
Claire: Real friends know that the world doesn't stop spinning just because they popped out a brat.
According to Clark (Claire's Fiance), Mary called Claire about twenty minutes later and a screaming match ensued. Apparently there was a lot of name calling, yelling and the beginnings of WW3 if Clark is to be believed. I'll probably end up getting the details of what happened a little later today or tomorrow but suffice to say that it appears the brown goo has hit the fan.
As for myself, I'm just trying to stay the ehell out this though Mary has called me once (while I was at work) and I'm sure she'll call me again wanting to say how terrible Claire has been to her. Not sure if I should ignore the calls or pick them up since I don't know if I can trust myself to keep my mouth shut.