I forgot how thick Rachel laid it on with Mark at the beginning
We all know how the Ross, Rachel, Mark thing will turn out and we know that Rachel never was interested in Mark while dating Ross but I forgot how blatantly she kind of threw it in his face at the beginning when she first got the new job and she found out Ross didn't really like Mark and like her with him too much.
When she gets the job, she's face to face with Ross but turns away to give Mark a big and rather long hug. Also, Ross wants to take her out to celebrate but she declines to have lunch (or dinner I forget which) with Mark.
It's as if she was trying to get under Ross's skin.