David Cassidy Explains His Health Problems at a Concert

David Cassidy hit the stage again, this time in NYC, and he was open about his medical and other problems.

David performed at B.B. King Blues Club & Grill Saturday night, and explained why he couldn't tour anymore. He's already revealed he's battling dementia, but also said he has arthritis bad enough that it makes strumming the guitar an ordeal.

The Partridge Family singer was super pissed at a woman who kept taking pics with a flash and ordered her out, suggesting she might be drunk ... a road he admits he's been down before.