The grinning maniac charged with fatally shoving a 76-year-old retired teacher down Manhattan subway stairs was once a talented Broadway dancer who fell off the deep end during the pandemic, a pal told The Post.

Rhamell Burke, 32, posed for pics with movie stars and was in the cast of the hit show “King Kong” on Broadway — years before police said he randomly pushed beloved ex-educator Ross Falzone down a flight of stairs at a Chelsea subway station last week, the friend said.

Rhamell Burke, 32, was a dancer on Broadway before he lapsed into mental illness, a friend said.…