Friends are not who they suppose to be

Hello all it's me again reporting in. This subject is about friends again sorry. Well I been friends with someone since 1997. We this friends as long as I have know her have had some issues with dealing with people. Now we are at the point where I can't even joke with her without her getting upset about it. The other day I just sent an email stating get to work I see you sleeping over there and her reply was F---U I mean jokingly I can over look that since we are suppose to be friends okay. If this person have a problem with some one joking with them they she should have put this out ahead of time since we been friends for a while now. I'm at the point with her that it is time to say good bye for good and let it be that way I tried this once before but I was told when you in a cliche you are stuck in it. I never knew I was in one well thanks for telling me ahead of time. Some time she will talk and other she don't so I'm still trying to figure out how I fit in with some one like this. In my opinion I don't I don't need the hassles that goes along with her Ego I guess you can call it that. She was once an Enlist and how she is an Officer well you think that has something to do with it, well maybe so maybe the rank has gone to her head and any case a friend is suppose to be a friend no matter what. Well I don't know what to do here but my Heart say let her go as a friend and wish her well with her life.