There was the Bridges case a few decades ago:
As a reviewer he saw a paper on rhodopsin metabolism in vitro and immediately realized its significance. He tried with some success to denigrate the manuscript thus delaying its publication. Meanwhile he rushed through some experiments of his own (later claiming they predated his viewing of the other manuscript) and submitted his own paper to Nature – which was rejected. Bridges denied all the evidence suggesting this summary of the events, but was eventually debarred from all Federal funding for three years.
And the episode last year when a paper on diet and obesity was rejected, followed by one of the peer reviewers republishing the results and manuscrpt as his own work:
