Before relating something negative, how about using the incident as a mirror; ask yourself, “Why did Hashem cause me to hear/see this? Maybe there is a hint to something I must work on.”
Check your underlying motivation in speaking; often it is arrogance.
Another tactic is to picture the perpetrator as a close friend or even as yourself. How would you view the situation in that case? Remembering mistakes you have committed comes in handy.
Check in for the next tip in the series next week!