Whilst there is no definitive proof where the Mexican ground karate meme came from, it is very likely that it was first mentioned on reddit.
The general gist of the Mexican ground karate meme is when relatives and members of your extended family ask you either which martial art you train, or how your martial arts training is going. Generally speaking, anyone who does not know about grappling has no idea what Brazilian jiu-jitsu is. Not only this, but they may have a low opinion of the grappling arts in general.
This leads to interesting conversations about BJJ and martial arts in general.
Phrases such as the following are not unusual between people that have never heard of BJJ who are somewhat intrigued by what you do.
“How is your judo going?”
“My daughter is 10 and already got her black belt, what color belt are you?”
And of course, the original the way the meme came about would have been something like this:
“What was that thing you did again, Mexican ground karate?”
Of course, there is no such sport as Mexican ground karate, although there are many Mexican people who train karate, some of which will have basic ground techniques. So, there is a convoluted argument suggesting that Mexican ground karate does actually exist in some obscure form.
However, if you overhear people talking about Mexican Ground Karate, you can guarantee it is by people who train BJJ and have spent too much time on the internet, like me.