1. Ad Hominem
This means "argument against the man, not the point". It's when you rebut an opponent's argument by insulting them instead of their argument.
Example:
"Your argument is wrong because you're a troll".
Even if it is true that the person in question is known for trolling, it does not invalidate their argument, the argument must be considered on its own objective merits, no matter who or where it comes from.
NOTE: There is a difference between an ad hominem and a plain insult. Saying "Your arguments are wrong because you're stupid" is an ad hominem, but simply saying "You're stupid" is not a fallacy.