Attack the speaker, not the speech. Recent studies show that cigarettes are making smokers’ heads explode. It’s a crisis! We must do something! Sadly, Doctor Smith says cigarettes actually do not cause heads to explode. You can safely ignore him because he must get funding from Big Tobacco. Right? Because Big Tobacco is evil. That means they lie all the time, right? And anyone who disagrees with the ‘cigarettes = exploding heads’ theory is pro-smoking, right? Actually, wrong. Wrong on every count. An argument of this kind called an ad hominem attack because it goes ‘to the man’ instead of to the idea. A scientific argument would not bother to note who funded Doctor Smith’s work. It would study his work instead. The scientific approach would be to look for and report evidence that heads exploded, and look for a cause that may or may not include cigarettes. That’s not as much fun as sticking it to Doctor Smith and Big Tobacco, so go ad hominem!