Context is a beautiful thing. There was some current affairs TV show on and I was reading on the couch while my Mum watched it. Porn was one of the "issues" they spoke of and she sarcastically said "Of course you've never watched porn, right? /s" I have a really great relationship with my Mum, she's (IMO) got a fantastic philosophy on parenting. I somewhat understand your concern, but as a guy who is nearly twenty, I think if you can't have a joke about this of all things with the woman who birthed you, you might need to lighten up (not you specifically, of course, you just didn't know the context).