Crab mentality is summarized by this line: "If I can't have it, then neither can you." I think crab mentality is not exclusively a Filipino phenomenon but a human phenomenon. It's driven by people's innate propensity to envy other people who are ahead. According to some Sri Lankans, the "crab" story originated there. In Australia, New Zealand, and Canada, they have a similar term called "The Tall Poppy Syndrome".
How do we cure this? Like all innate tendencies like greed, gluttony, etc...we can only discourage it or keep it in check. I mean, if a corrupt politician uses that line of defense (that those who are accusing him of corruption are just showing crab mentality), then how are we supposed to run after these people? If there's one thing that experience ought to teach you is this: Do not see life as merely black and white. There are gradients in which some measure of suspicion should be warranted.
Look at what politicians are doing nowadays. Every single one of them who's about to get investigated will cry "crab mentality". That should sound very strange in a country where everyone agrees that corruption is rampant. But when we want to investigate, everyone ends up innocent and those who want to investigate are crabs. So which is which? Is corruption a problem or not? Since there are no government officials in jail, THEREFORE there are no corrupt politicians. THEREFORE corruption is not a problem in the Philippines. Problem solved!
* By the way, I have to correct the guy who stated that the Spaniards ruled us for 500 years. The Spanish era is a period from 1521 to 1898 (377 years). But if you consider the present day as no different from the Spanish era...then of course you can look at it like that.