How do I react to this?

Over Thanksgiving break, my boss had seen that I left my Facebook open at work by accident. As a punishment to being on Facebook at work he decided to log in as me and posted a sonogram stating I was pregnant (I'm not) and even responded to commenters.
When I saw the posting I immediately apologized to everyone telling them it was not me and I did not know what was going on. He then responded as me stating that it was the wine and that I was due in the spring.
When I returned to work I was approached by the co-owner and the manager who took his side that it was not ok to be on Facebook during work hours even though it was widely known that we use it for both personal and business use. I am no the only employee who uses it and I have never been approached about it prior to this incident.
The meeting then escalated when I said it was not ok that this happened to me and it was clear that my boss was right and I was wrong so I quit.
I do not know how to handle this situation?
How do I react to this?
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