A while back, I believe that I made a short post about how it's kind of comforting the first time you hear someone say something mean or swear or fart or do something that a lot of people normally don't do around strangers or in mixed company. They've decided to let down those barriers; they have at least some slight amount of trust in you. You've gotten to know them at least a little. (I vividly remember writing this post, but I can't seem to find it with a cursory search. That was the gist of it.) I remember the first time that the nice older man who is part of the Thursday gaming group used the phrases "butt plug" and "evil fucker" within about a minute's time; I thought it was hilarious.
I've noticed that someone else that I know somewhat well has done the reverse. He's actually become more timid and polite and guarded over the past few weeks. Normally I would associate that with the person being uncomfortable around me, but I really don't think that's the case. I don't think that he thinks that I would be offended (I'm quite fond of the phrase "dirty bastard" while playing games) and it's not some super-conservative Christian upbringing because (1) I know for certain that he's not Christian, and (2) he used to swear. Maybe he's got a girlfriend trying to get him to shape up or something. Maybe it all just depends on the week that the other person had. Maybe it depends on body language that I don't know I'm giving off.
Or—and this is fairly likely—I'm just reading too much into things again.