Someone who doesn't actually practice a martial art of any sort, but loves to comment on them like their an expert. Quite similar in concept to that of a backseat driver. They tend to obtain most of their martial knowledge from internet video clips, free TV airings of fights, and sometimes they might even spring for a pay-per view match. A common favorite move of the backseat martial artists to try and perform is the armbar, which they typically learn from watching old clips of Royce Gracie and not from an actual dojo.
Once only staunch supporters of BJJ, they have now decided to extend some of their divine credibility to that of Muay Thai.
Person: What kind of kung fu should I take?
Backseat Martial Artist: Take BJJ
BMA2: Grappling is the most effective form of fighting, therefore you should definitely try to use it against multiple opponents.
BMA3: That won't work in real life, trust me I know
BMA4: Well in a real fight............... *5 paragraphs of bad spelling later*.... and thats why you should take BJJ