A person who scuttles along the platform as trains come to a halt, trying to be in front of the nearest door, giving the best chance of getting a seat. Sometimes results in humiliation when the train pauses then moves a few metres further, meaning the whole exercise was pointless for the crab. Hardcore commuters have the right to tut as this goes on, as of course they know exactly where the door will be and don't need to scuttle.
Whilst standing at Finchley Road in the morning chatting to a friend as a crab approaches, "Damn here comes a Platform Crab, I'll just strategically place my briefcase here to end their scuttle"
by Sam Crawley September 09, 2005