this joke will go awry someday

So I don't really know what started this, but not long after my traumatic brain injury, I started continually making references to the "fact" of mom using lots of illegal drugs (she doesn't-- that we know of (we're still looking)).  It became a common joke in my immediate family that mom's a crack addict, or name any other drug, such that she's always hiding the needle marks on her arms, theories as to where she hides her stash, etc.
Now this joke almost took a bad turn about a year into my brain-recovery.  We were eating lunch at a table at some fast-food restaurant.  In comes a police officer in uniform, and he gets in line.  Keep in mind that this is REAL EARLY in my brain's recovery, and what I thought was funny just kinda isn't.  So I stand up, walk over to the officer, and flat-out say "Excuse me sir, would you arrest my mom for drugs?"  Since mom could still hear me, she almost choked on a burger.
Don't get worried-- he just chuckled, said no, and told me to take care of her.  Now I see the error in my ways: using the word "mom."  Sheesh, if I'd just said "that lady over there", it'd be wham, bam, thank you ma'am, and mom would have bunked down for the night with Big Sue in the big-house.  The TBI's evident since I still think that's at least worth a chuckle.  But I know much better now about this kind of humor-- best to keep it almost entirely private (inside my head, to dad, and on my blog only).
But that didn't stop us from making continual private references to mom's "habit" ever since then.  And it reached a pinnacle today when mom was incredulous at something I'd said, and asked "Are you into my crack-cocaine?"
WOW.  Just shy of a an ending involving the phrase "visitation hours", this is as far as a joke can go.  When the person the joke's about starts making the joke themselves, you have accomplished something.  Not sure what, but you've accomplished something.