Proof By Assertion

The simple art of repeating one's argument over and over regardless of whether one has any real evidence to back it up, and indeed, whether the argument has been completely demolished by evidence from the opposing side. More than one Internet debate has gone this general route:

Rick: "There is absolutely no evidence for my opponent's claim that apples grow on trees..."
Lacy: "Actually, you're wrong." *shows evidence*
Rick: "Okay. But there is still no evidence for-"
Lacy: "I just showed you the evidence!" *shows more evidence*
Rick: "...As I was saying, there is no evidence for my opponent's claim..."
Lacy: "What about this?" *shows yet more evidence*
Rick: "There is still no evidence for your claim."
Lacy: "Forget it. I give up."
Rick: "My opponent withdraws! I WIN!"

Obviously, Lacy giving up on trying to persuade Rick doesn't mean that she's wrong about apples growing on trees, though Rick and his supporters will take it to be so.