Ian, the Perfect Dark one is pretty stupid, but I think that's more forgiveable than the woman who didn't understand that Mario was a Nintendo franchise.
Not to defend your friend's stupidity (since he was clearly wrong) but in retrospect we can see that Rare wasn't going to stick with Nintendo forever, plus, Perfect Dark was a new franchise (heavily based in the GoldenEye engine doesn't really count), and shooters seemed more fit for the demographic that PlayStation owners supposedly are rather than the N64 (ignoring GoldenEye here I'm not sure about, though).
On the other hand, a woman who has three or four children, including one that's supposedly 11 years old, must certainly be old enough to have lived through the 1980s and 1990s, in which time Nintendo was synonymous with video gaming and Super Mario, being the chief Nintendo mascot for all that time (and still is), was and is synonymous with Nintendo. With all the Mario spin-offs, it should still be hard to ignore or be mistaken about, when Mario's bright red and blue are lavishly visible all over the Nintendo sections.
Then she could've lived under a rock all that time, but hopefully she simply misheard her son (though why she didn't call him to reconfirm since she had a cell phone, I'm not sure, and the person who wrote that noted that as well) and that the son does know where Mario belongs, otherwise we already could have a generation of people who don't understand where Super Mario's home is. Her refusal to even look at the section where the employee, manager, and employees at another store were all telling her repeatedly to check out is the kicker - there's "not-knowing-the-obvious-facts" stupid, and then there's "not-listening-to-what-everybody-is-telling-you" stupid, and she's both.
While working at Playdium a few years back, I encounted many-a-stupid person, at every position I worked at there, but I was mostly a front admissions cashier and then a supervisor, both of which had to deal with many not-too-bright people. I expect that not everyone "gets it", which is fine, but I get peeved when someone who "doesn't get it" doesn't even try to. Maybe the "listening" part of their brain breaks down under the slightest bit of frustration, or the other explanation, which is quite sad, is that some people are willingly choosing to be ignorant.