[gjm11]

Do you mean this one? It's the only one I can quickly find that includes "math enthusiast" and "mathematician", though it's not exactly "how to tell the difference". http://www.smbc-comics.com/index.php?db=comics&id=2320

[dylangs1030]

Yeah that's the one! I probably should have just googled for it, but yep, that's it. My memory was a bit hazy.