An ex-con member of the “Billy Bad Ass” gang was busted in the random assault of a 70-year-old straphanger aboard a Manhattan train Sunday, police said.
The elderly victim was riding a southbound A train through the 145th Street station in Harlem around 11:30 p.m. when two men – including the 27-year-old criminal on parole – stormed up to him, cops said.
One of the men — both strangers to the victim — punched him in the face for no reason, cops and law-enforcement sources said…