'The Bump' Handshake?

During the last few years "the Bump" (touching fists knuckle to knuckle) has become popular. I am told this "handshake" originated in gang culture, but my shushi chef has been doing it for 20+ years (it prevents the spread of germs). I'm sure in Japan the people simply bow, but is this considered 'Sushi Etiquette' in the west? My friends say no, but I'm pretty sure my sushi guy doesn't know any gangsters. Has anyone else any experience here? There's money on it, so I need a source.