Quick Game of: Would you be offended??

So this morning my baby is in his walking ring exploring as he usualy does under my watchful eye. He starts pulling on the Laundry basket so I take a hanger and tap on the washing machine to make a noise and say no don't do that. At the same time my Mother In-law walks in and says... (wait for it...) Don't do that, it is domestic violence!!!!! I let it go the first time she said it. Then when my husband was done getting ready and joined us she had to mention to him ( in a joking wat) like that is something to joke about. Talking like she is my son. "Daddy I witnessed my first domestic violence" needless to say I was not happy and decided to rather remove myself from the situation then make a scene but she could see I was upset. I went on with getting ready for work while the two of them played om with my son. When I joined them again my Father inlaw was walking towards us and again she said same the same thing to him. That was it. I lost it!! I said that is enough and that it is not funny. Everybody took her side and said it is just a joke. When I re-entred the room it was just hubby and Father Inlaw. she had left. So here is the question. Am I to easily offend? Am I wrong to have spoken up?