I think it's a form of Tourettes. I find myself in a moment - could be anytime, anywhere, anything - and my mouth just says the STUPIDEST thing possible. My brain then realises what my mouth just said and disowns my entire body.
Example - I just stopped at the bottle shop for a bottle of wine and packet of smokes (yeah, I'm all class, me) and while waiting my turn to pay I find myself mildly amused by the hand-stitched tiny white curtain blocking the cigarette packets from my view, so I decide to light-heartedly comment on said curtain to the rather hawt young dude at the counter. It went a li'l bit like this:
Me: Oh, cute - you have to hide the cigarettes now?
Him: Yeah *checking out hawt young girls giggling at 6 pack of Cocksucking Cowboy shooters*
Me: Erm, did you make that curtain yourself?
Him: No *checking out anything except me*
Me: Hahahahahaha, no, I suppose not. *cringing inwardly and wishing large hole would appear beneath my feet*
Me: Ah yes, I remember when they cost less than a dollar a packet *said in wistful tone with deep sigh*
Him: Um, ok - that'll be $35 please
Me: *presses Eftpos buttons* *runs away very quickly*
Oh yeah - that was smooth, T! Let's firstly accuse hawt dude of being a secret curtain-maker, then let's dismiss that offhand as though it's unmanly, even though it really isn't. Then let's follow up with another comment that just covers all the bases - I'm roilly, roilly cool 'cos I've smoked since the dark ages and oh, yeah - I'm really fucking old, too.
*sigh* I felt so fucking stupid it reminded me of the time last week at Woolies where I was doubled over, legs crossed, battling through a coughing fit (flu-related, not smoking, I swears), looked up and caught the eye of a couple of skinny teenaged girls in jeggings looking at me and commented "yeah, you go and give birth to 3 big-headed babies and then tell me how perky YOUR pelvic floor is..."
Sometimes I wonder why I let myself leave the house.