Context: I don't have too many friends at my office and it's not because i'm not friendly ,it's just that most of the buddies i had ,have switched to other companies over the past few months. Of the few i still have, two are particularly close, one guy and girl. They are pretty helpful for the most part and we hangout frequently. The girl, let's call her Katy, has a vicious side to her where she often makes fun of me for being slightly chubby(BTW i'm a guy ). 

I have always let this slide and taken it on the chin, but i can't help noticing Katy isn't a perfect size 0 either. I'm not condoning unhealthy body types, too fat or too thin and i agree i should get into better shape. However it's gotten to the point that Katy points this out at every opportunity she gets. 

Yesterday another friend of ours, Kevin ,mentioned that there was a free for all marathon next week and asked if we would like to join in . Katy joked about how i should join first so i would burn up some of the fat I've got "stored in my cheeks". It bummed me out.  The worst part of this.. she laughs this off and never ever apologizes.

At this point,i should mention, I've known Katy for a couple of years and she has been a great friend for most of that period. It's just that i feel i should give her the taste of her own medicine by letting her know that she's not in shape either and maybe i'm not the only one that should be hitting the gym. Another part of me thinks that this would be a cheap-shot.

TL;DR: Female Colleague keeps poking fun at my weight while being on the healthier side herself 