Nicki Minaj isn't backing down after controversially calling Don Lemon a homophobic slur ... she's doubling down on that remark in a new podcast promo that dropped amid his arrest. Days before Don's Thursday night arrest, the rapper sat down for an interview on "The Katie Miller Podcast" ... and she was asked to respond to him calling her "racist, unhinged, homophobic and our of [her] depth" -- all comments he made on "TMZ Live." Minaj replied simply, "C***sucker, stop" ... prompting laughs