Mark Dohner

Rob Gronkowski's smokin' hot GF says modeling agencies pressured her to drop serious weight in order to get gigs ... but the NFL superstar urged her to not give in to their demands. Camille Kostek said Gronk made her realize she shouldn't have to conform to the crazy, unrealistic standards in…

KSI is in some SERIOUS trouble come August 25 ... so says Logan Paul's old roommate, Mark Dohner, who tells TMZ Sports he knows firsthand what the social media star is capable of doing. Dohner -- who has more than 2 MILLION subscribers on YouTube -- says he's had his fair share of scuffles with…