I have never seen people say it was a failed experiment when it "disproved" a hypothesis. If it was able to disprove something, often that means people perceive a high degree of certainty in the results.

They might be bummed out and try to suppress its publication because they don't consider it disproof of a favorite theory, though (for whatever reason, good or bad).

Edit: I just remembered that one time I saw people complain that their analyses had "too much power", which might fit in with the parent comment's point?