The ex-Broadway hoofer charged with fatally shoving a retired teacher down Manhattan subway stairs posted an ominous online message last year before he went off the rails with a string of unhinged busts. “Sorry, I had a MANIC EPISODE,” Rhamell Burke, 32, wrote on Facebook in July . “Do U still wanna f–k me?” About six months later, in February, the once-promising performer was then hit with the first of what would be four bizarre arrests before being charged with murder in the caught-on-video push of 76-year-old former educator Ross Falzone at the 18th Street station in Chelsea on Thursday. Rhamell Burke’s bizarre Facdbook post in July. Just months later his spiral downward began. Ghouls & Gals / Facebook Rhamell Burke, 32, is charged with murder for allegedly pushing retired teacher Ross Falzone to his death.…