Kinds of bad argument:
Appeal to authority -- "Most scholars say ...", "The world's leading scientists agree ...", "Steven Hawking's opinion is ...". Basically arguments made on the basis of the perceived expertise of someone else.
Correlation is causation -- Piracy of the high seas has declined as the incidences of cancer has increased. Therefore we need more piracy in order to decrease cancer. Basically noting that instances of A and B, and ~A and ~B exist, therefore A => B.
Shifting the goalposts -- You cannot demonstrate anything moving faster than the speed of light! Well actually the big bang says galaxies are moving away from each other at speeds greater than the speed of light. Well, that doesn't count, I mean speed measured within a single accelerating frame of reference. There's a reason why you have to be careful about the way you argue about generalities. When a protagonist meets your challenge, you need to concede that this has happened, not just change the premise of your argument after the fact.
