She's an athletic girl, but she wants to insult a jealous, mean skinny girl?

maybe this girl has an eating disorder or is fighting some other battle you cannot see. Have empathy(sympathy?) for her, do not make jokes about her, don't lower yourself to her level, show her and others that you are better than to make fun of a weak person, seriously just ignore her or offer to help her with her work outs... be the bigger person..

I hope for your sake you're not 25-29 like your age range says, because this sounds like petty high school sh*t, not something two adults would engage in.

Wow, that is so lame and too much drama. There is always going to be loser like that in life. I would just smile and live well. If she needs to say something, she should just ask "are you jealous of me? If not, why do you need to open your mouth? You should talk about and to me when you are on the same level as me."

I am skinny and I don't like how you generalize because I have both skinny people and fat people that judge me. I stay positive and ask them "I like to stay health. Would you like to join me at the gym at 6 am tomorrow? I exercise at least 5 days a week for my body. :)" That shut people up and no one lazy ever take my offer. Oh well.

Part of being a good boyfriend is encouraging your significant other to better themselves. This is a golden opportunity.

Don't get involved & suggest your girlfriend do the same. Cut her (the ex-friend) off. Nothing good comes from communicating with, as one person put it, "jealous bitches."

Sorry to say but the only way to win this IS to ignore her, her friend is nothing but a silly, immature drama queen who has low self-esteem issues, is there honestly really anything to gain by delving into drama that will only make you both unhappy and constantly feeling angry at this girl?, don't be silly and see that that girl is just doing it for attention because she lives in so much self-pity, I have been friends with a few of these types of girls now and all your doing is keeping the first going in a never ending battle, ether of them are going to win all they are doing is making themselves look stupid, think about what influence she is having on herself and how she is encouraging those around her by also acting immature by constantly having to win. My bro is the same way but 10 times worse and all it ends in is one of us in tears, so for sure just walk away, she is not worth all the tears and feelings of angryness, focus on just what makes you happy. If your girlfriend is so happy with herself why does she still feel the need to compete with her? lol.

omg why are you involved in this silly petty female drama? it's bad enough we act like this I expect more from men...sigh...girls are hateful jealous bitches this is something by the time they are your age they should just ignore but some women never grow up and act like adults they wanna fan that flame and keep this sh*t going on into their 60's. Sometimes I hate my own gender I swear I do.

she should let her talk and make a fool out of herself cause no adult is going to think this is cute.

Jealousy is always a bad thing. Just don't get in the middle of a cat-fight over this because they will team up and make you look bad, trust me. Support your girlfriend in her training and just let the other girl do her thing.