Here is some good advice from Dave Ramsey about how to act online:
Don’t post a picture or write something in social media or in a comment on an article that you would not be willing to put on a billboard on the highway. If you don’t want your mother, grandmother, church leader, future college admissions counselor, or future employer to see it, don’t post it.
Think before you write something about other people. If you wouldn’t say it to their face, then don’t post it.
The medium is not an excuse for a lack of courtesy or propriety.
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