Ad Hominem

Logical fallacy

Attacking the person advancing an argument rather than the argument itself. Their character has no bearing on whether their reasoning holds.

An everyday example

“You failed maths at school, so your analysis of the budget is worthless.”

“You're a preachy vegan, so there's no point listening to you.”

Addresses the people making the argument rather than the argument. Their manner is not evidence about the conclusion.