Southerner here wrote:
Yes. Ever heard of getting what you give?... I have great relationships with my colleagues, hence them knowing no skinny-joke will go unchecked.
Honestly, unless they are being brutal, I would assume those who are commenting on the OP's size are likely just joking around and welcoming you to the circle, so to speak. At my first job out of college, I was around 16 shift workers (chemical plant) at any given point in time who were ex-high football players that now sat 11.5 hours out of a 12 hour workday and devoured fried chicken in between smokes; they were unhealthy, and they knew it.
They harassed me my first week, playfully, until I - the 22 year old kid - asked one of them if there hip was hurting. When they confusedly asked, "No. Why?" I replied, "It looks like it's about to rain and I know how folks your age get when the weather changes. Just making sure you didn't need a Tylenol." They all died laughing.
From that day on, I wasn't the "new kid"; I was "one of the guys". Mind you, the gentlemen this was directed at was the Union steward for the site and 30 years my senior. He'd seen me open the door for folks and always reply with "Yes sir" and "No sir". He knew I was respectful and knew I meant nothing by the comment or any of the ones that followed in the 3 years I worked there. He looked out for me, helped me multiple times when my role required an almost managerial role with several folks who had no direct reporting to me, and is still a friend I keep in touch with.
So many people these days take themselves too seriously. Learn how to read people and read the room and you just might find that people will accept you into their circle; take it too seriously, get offended, and it's a sure fire way to be the object of spite.