File this under why-we-can't-trust-anyone-anymore: the Post sinks its teeth into the tragic story of panhandler Robert McMahon, the one-armed Vietnam vet who can be seen hobbling for change along Ocean Parkway in his combat fatigues. Except that he's not really a Vietnam vet. And he has both of his arms.

A Post photographer snapped a shot of McMahon with both arms out after a day of begging for change, and they were pissed at the scam: "he carries on with his wounded-soldier act, day after day, weaving through traffic and occasionally cursing out people who refuse to give." They discovered that there's no record of him in the Marines or in Vietnam, and he has a rap sheet of 20 arrests, many for disorderly conduct and "fraudulent accosting" (aka, being a scammer). "He's been doing the fake-arm thing for at least 20 years. He's crazy as a bat. Everyone around here knows about it," said Robert Gainey, a vet who did two tours in Vietnam.