It’s no secret that the YouTuber Leroy Truth, who has dedicated more than half a yearto attacking Union City Mayor Brian Stack, has gotten under the mayor’s skin. But last week,Stack brought his constituents and mayors Steve Fulop of Jersey City and Nicholas Sacco of North Bergen into the fray via a letterto the community titled “Please Put Yourself in My Shoes.” Fulop’s response — which included some medical advice — was biting. The letter, never named Fulop or Sacco, instead referring to Fulop as “a candidate who has statewide political ambitions” and Sacco as “an outdated political boss fro…