Do you think that they're being immature?

Well I broke up with my ex maybe a week or so ago but we had never stopped talking, and it was like before. And it wasn't helping either of us with all the contact. So I told them that maybe we shouldn't talk for the time being so we could give ourselves time to move on. Now before we broke up we were close friends. I popped onto their Facebook and find they have made comments, publicly, about me. Insulting ones. So I decided to talk to them about it and they told me I can't take a joke. Now, I am pretty sure I can, there's a difference between a joke and public insults. Is it just me, or is this a bit childish and immature?