This situation has already come and gone for me, but I'm looking for advice on how to handle it if it were to ever arise again.
I worked at a small company of around 25 people in which the CEO and CTO did not see eye-to-eye. This created a toxic workplace and I successfully found a position at a different company and put in my two weeks notice. So far, so good. However, as someone who worked directly under the CTO, I frequently had lunch with other employees who worked under the CTO. During one such lunch outing, my co-workers were discussing a plan on sabotaging the company's yearly user conference by vocally airing some of the CEO's dirty laundry at said conference. I wish that they hadn't done so in my presence, but as they did, I informed the CEO of this plan as it did not sit well with me at all and they wound up not being allowed at the conference. My last two days of employment were rather uncomfortable as a result.
My question is: Was my behavior here what you would expect from a professional? Should I have left it alone?