Coworker dilemma.

So, I hate when work becomes like high school...and things get blow out of proportion.  This situation is very high school, and I apologize in advance.  Here's the situation....we have a coworker that we all (a large department but only about 9 of us were promoted to a specialty position).  This coworkers "head has grown" significantly over the years so the person believes no rules apply and they can make own policies and procedures...their position essentially is above manager (even though it's not).  The person gets on our case about lunch but then goes to lunch when it's convenient.  Long story short---I finally discussed with an actual manager the concerns of myself as well as others.  This coworker is talked to.  I now just got a text message from that person saying thanks a lot for telling and that it's so high school.  I don't really know how to respond.  I would like to tell the coworker it's not just me and that other people have said things too....but I don't want to drag anyone else into this, but this person needs to know their attitude needs to change and that we are all in the same position.  I don't know why I said anything ....ugh.