[robben1234]

Create a group chat with all contacts containing 'ex' in the name/comment. Send 'sup losers' to the chat, leave the chat.

[ghostly_s]

If only "leave the chat" were a real iPhone feature...

[Jtsummers]

It is with iMessages. Not sure if you can leave one you've started, but I've left some that others have started (my email address was similar to their friend's).