"There is no piece of evidence which evolutionists would accept as disproof of evolution theory. This proves that they're being dogmatic. Scientists won't even say what they would accept as proof! When questioned, they have no answer and try to change the subject! What does that tell you?"

This is a rather amusing argument since it's a spectacular case of psychological projection: they are projecting their own "fixed conclusion regardless of the evidence" mentality onto scientists.

In reality, scientists are hardly at a loss for words when challenged for falsification criteria; Darwin himself outlined two potential disproofs of evolution more than a century ago:

• A feature on some species which is not similar to any feature on any other species.
  
  
• A feature on some species which exists for the exclusive benefit of some other species, with no gain to itself.

For example, if you could show me an organ in the human body which is not similar to (or identical to) an organ found in other primate species, you would have disproof that we evolved from older primates.

The problem is not that scientists refuse to define criteria for disproving evolution theory; the problem for creationists is that scientists did define such criteria, and in such a manner that they would not be difficult at all to meet (no "go back in time 4.5 billion years" nonsense, unlike similar creationist demands), and creationists have simply failed to meet them.

Fallacy watch:

• Outright lie (technically not a logic fallacy, but there's simply no other way to describe it: there is no part of this argument which is even partially true).