Bad grammar?

Jack's wife Becky and I met with a former professor for lunch yesterday. Yes, we're that nerdy. Our pastor once told me, "You're taking 'teacher's pet' to a whole new level." Granted, we were decorating his office with tacky Christmas "ornaments" almost a year after having graduated from school. But what can I say--it's an annual tradition now.

In any case... this professor, who is almost certainly the most challenging professor at the school and who has extremely high academic standards, suggested that he is increasingly uncomfortable using the phrases "good grammar" and "bad grammar." I was shocked. If there is anyone I would expect to be a stickler for calling proper speech "good" and denouncing more casual speech as "bad," it would be he. I mean, he once sent me a series of e-mails ranting about the use of "whether" instead of "if." (I kept making the same mistake, just to bug him.) But he now says that instead of "good" and "bad" grammar, we can only refer to the acrolect and basilect (here's mesolect, too, just for good measure).

Thoughts?