This was the best example by far IMO: A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal." B: "Well, you're a rodent and

This was the best example by far IMO: A: "All rodents are mammals, but a weasel isn't a rodent, so it can't be a mammal." B: "Well, you're a rodent and a weasel, so there goes your argument." B's argument here might appear on superficial inspection to be sound, but it is in fact ad hominem. He is using the terms "rodent" and "weasel" in different senses to those used by A. Although he tries to make it appear that he is countering A's argument by invalidating one of the premises, he is in fact trying to counter A's argument by heaping abuse on A. (This might also be an example of an *ad homonym* argument.)