Rob Kardashian & Mama June -- Only One Has Lost 100 lbs.

Reality stars Rob Kardashian and Honey Boo Boo's Mama June have guts ... to be so public with their weight battles.

Rob -- who has been working out hard trying to lose the 40 lbs. he gained since his breakup with Rita Ora -- showed off his manly curves in a clingy white t-shirt at the Clippers game in L.A. last night , while Mama June proudly showed off her slimmer physique on Wednesday ... after dropping 100 lbs. from not dieting and not hitting the gym.