Typically this term refers to a rhetorical strategy where the speaker attacks the character, motive, or some other attribute of the person making an argument rather than attacking the substance of the argument itself. This avoids genuine debate by creating a personal attack as a diversion often using a totally irrelevant, but often highly charged attribute of the opponent's character or background. The most common form of this fallacy is "A" makes a claim of "fact," to which "B" asserts that "A" has a personal trait, quality or physical attribute that is repugnant thereby going entirely off-topic, and hence "B" concludes that "A" has their "fact" wrong - without ever addressing the point of the debate.
"you are such a Shmuley". "you are acting like a Shmuley". "He/she is being a Shmuley". "They Shmuley everytime"