First idea: check if the proposer uses the techniques of rationality and science. Does he support claims with evidence? Does he share data and invite others to reproduce his experiments? Are there internal inconsistencies and logical fallacies in his claim? Does he appeal to dogma or authority? If there are features in the hypothesis itself that mark it as pseudoscience, then it's safely dismissed; no need to look further.

More:

Does he use math or formal logic when a claim demands it? Does he accuse others of suppressing his views?

The Crackpot index is helpful, though it is physics centric.