I actually have grown to like JAG. At first it bothered me a bit, because we were writing off a guy so quickly as a "jag" who hadn't even played a snap of preseason football.
But now it kind of fits as a dual purpose anagram - his initials, and also meaning "just another guy", but in a chip-on-your-shoulder motivational sort of way. He is "just another guy" from some unknown small school who people wrote off fast, and now he can show them why they're wrong, potentially.
Brady forever remembers being the 199th pick but wears it as a badge of honor by having proven everyone wrong, Jimmy can encompass the same idea with the "JAG" moniker. Just my two cents.