What are signs to you that someone is dangerous? Not in a physical sense but in other ways?

For me, the biggest red flag for someone dangerous is someone who completely flies under the danger radar. The person who gives up NOTHING of what they are capable of, or what sort of danger they represent to me.

Going through other answers, I think I can explain better.

If someone is manipulative, I recognize that I may be seeing and hearing what they think I want to see and hear, and thus, be on guard for any sort of jockeying they are trying.

If they ask a ton of questions (fishing for info), I recognize to look for relevance to them or usefulness of the information (what does having this knowledge DO for you?), to further analyze motivations and potential issues.

If they bring out the bad in me... (for me, that's an interesting beast to open the cage and let out-- I keep it locked up for a reason... so...good luck with that...! Just a helping hand, if you are bound and determined to be this person-- do NOT show any sign of fear or weakness. Unlike a cat, it doesn't PLAY with it's prey, and the second you show fear or weakness, you just put on the shirt that says, "PREY" in bold giant neon letters...) I recognize that I have a kindred spirit running with me, and our devils shouldn't be allowed to play with each other. At least, not in public.

So, with each of these examples, they are doing something that gives me notice to be on guard. It's the one that doesn't give me notice I am concerned with... for they are playing things so close to the chest, I can't get a read.

THAT is dangerous. ;)

They like pineapple on pizza

When someone talks about how honest they are, again and again, I start to question their honesty. And when someone avoids my questions, I tend to suspect that they know that I wouldn't like the answers. So I guess for me, evasiveness and bragging about how honest they are. Also, if they NEVER tell me anything that I don't want to hear, that can sometimes be a red flag too.

And one other thing. If they gossip about others, that makes me wonder what they might be saying about me behind my back. And when someone talks about how terrible everyone is that they've ever been involved with, sometimes I start to wonder about them, unless I can see that they're attracted to toxic people. One should keep in mind what the one constant is in all of their stories

They break the law all the time or show blatant disregard for it.
They threaten to harm you and you know they mean it.
They have a history of animal abuse.
They blame everyone for what is wrong in their life.
They manipulate.
They say they have nothing to lose as a justification for what they do.

the person brings out the bad in me

Manipulative

They ask a lot of questions lol 😆