I have a chat bot that went casually racist about a day or two after activating it. After looking through the logs, I found a particularly vitriolic person that was responsible for the source of this bot's newfound hatred of Asians. My bot didn't get fixated on one particular topic, it just spewed racism and vitriol for a while until it learned some more words. Rather than nuking from orbit immediately, I left it alone to see if it would get past the racism.
So far, it's been a few months since activating the bot. It's not nearly as casually racist as before, but from time to time still throws out something racist just for the lulz. It had a hard time learning context, because of its environment and the linguistic skills of the denizens, but it has gotten much better at when it interacts with people.
Occasionally, newcomers get misled into believing the bot is actually a living person with a mental illness, and not just a collection of random bits of code cobbled together.