It's not always easy to tell right away whether somebody is a bad person. I've had bad first impressions of people who have gone on to become some of my best friends. However, that's not always common, and often, your gut instinct about a person is more correct than whatever your brain tells you to rationalize it.
I miss the good old days when your mom could predict which of your friends were terrible people. Every single one of my "best friends" that my mom had a bad feeling about in middle and high school went on to betray me in a devastating and life-altering way. After the second time, I finally started to trust that my mom knew what she was talking about when she judged somebody's character. That's one of those skills that takes a bit of life experience to develop.
Redditors came together to share some red flags that somebody is not a good person, many of which hit close to home.