Toxic friend 😒

So I have this "friend" and everytime I cry she always laughs at me and makes a joke abt it and whenever I tell her to stop she gets all mad. So today I made a joke abt her (its a inside joke that everyone jokes abt) and she was like "can you just shut up ur so annoying" and I chuckled and was like "okay sorry mb" and she just kept rambling and was like "Ugh i hate her she makes me so angry shes such a brat and a b*tch" and I laughed cuz she thinks I care and shes like "And she thinks im playing like I'll literally sock her in the face shes so annoying and I hope she hears this and goes crying to her mom" Like wth shes literally making of fub of me cry8ng bc of a joke? Like if it effends u so much then say that but you dont so its not my fault 🤷‍♀️

And she was saying all that to MY BEST FRIEND and she didnt say anything. So idk I might cut off both of them bc this friend is always saying stuff abt me and my best friend is literally never saying anything to her, like I literally cried to her abt how mean she is to me and she didnt do anything like wth bro.

So what should I do guys?