Aw maaaaaaaan. The Senate colleague who told Sen. Kirsten Gillibrand (D-NY) not to "lose too much weight now" because "I like my girls chubby" was reportedly the late Sen. Daniel Inouye of Hawaii.
Daniel Inouye Is The Senator Who Called Kirsten Gillibrand 'Chubby': The New York Times
Gillibrand shared the story in her new memoir Off the Sidelines, talking about how her male colleagues in the Senate felt free to comment on her weight -- most egregiously, the remark about "chubby" girls accompanied with a squeeze of her waist. Gillibrand declined to reveal the name of the colleague in question.
According to The New York Times, it was Senator Inouye:

