(also known as: counterfactual fallacy, speculative fallacy, "what if" fallacy, wouldchuck)
Description: Offering a poorly supported claim about what might have happened in the past or future, if (the hypothetical part) circumstances or conditions were different. The fallacy also entails treating future hypothetical situations as if they are fact.
Logical Form:
If event X did happen, then event Y would have happened (based only on speculation).
There you go, meathead.