Yes it's an abusive ad hominem, and it poisons the well to boot. No, that is not an acceptable form of argument. (Other answers cover those fallacies in more detail.)
The logical reason is that even if we were to suppose that the abusive claims were wholly true, so that B had faulty senses and lacked ordinary skills, that personal fact would have no bearing on the question of the relativity of social understandings and customs in general. B could have a million faults, but the argument isn't about personal faults, it's about a general phenomenon. A more extreme example:
X: 2+3=4
Y: No, the sum would be 5.
X: Sorry, but everyone knows that you're an imbecile.
Yet the answer is 5, the abuse can't alter that.
Note that even if the answer were something else, the abuse would still be irrelevant. Modifying the example:
X: 2+3=4
Y: No, the sum would be 6.
X: Sorry, but everyone knows that you're an imbecile.
The answer is not 6, but the abuse doesn't advance the argument.
Finally, suppose X is correct:
X: 2+3=5
Y: No, the sum would be 4.
X: Sorry, but everyone knows that you're an imbecile.
The abuse is still irrelevant. It doesn't attempt to prove or disprove the disputed arithmetic.