Technically, Robin and Barney broke up on their own, but Lily was definitely determined to be the catalyst so yeah, her actions really, really irked me. Why couldn't she simply talk to Robin about her relationship with Barney like a grown woman instead of going behind their backs and manipulating them like a catty teenager? I mean, seriously, she broke them up because Barney got fat and Robin got frumpy? So what? Hate to break it to you, Pumpkin, but most relationships go through a frumpy phase at some point. That's just life.
It was a crap সরানো on Lily's part and if a friend did that to me, I definitely wouldn't be trusting her again any time soon.