You might be toxic if:
You gossip a lot and you just can't help yourself. The majority of the time it's something negative about a person.
You act like you are too good for most people. You prefer to hang out with those you see as your near equal.
You envy or get jealous even of people you don't even know. Oftentimes, you believe that that should be you and not them.
You unreasonably see some people as a threat to your own beauty, money or general success.
You hardly mind your own business. You often try to extract or find negative info on someone so you can gossip or make yourself look better.
You don't like it when others are praised. It bothers you a lot because it isn't you or you think they don't deserve such praise.
You might be okay with your friends being successful as long as they aren't more successful than you.
You view every single one of your exes as "crazy" or horrible human beings. This is a good indicator that you see things in only black and white, and that you don’t think you are to be blamed or responsible for anything.
While in a relationship:
You're with your partner only because of some benefit that you are receiving from them, whether that's money, a place to stay, social status, attention, etc.
You cheat or lie A LOT. Duh, right?
You often try to exert control over your partner. "Don't go there," "Don't talk to them," "Give me your phone." Of course, this never applies to you.
You gaslight - you attempt to overwrite your partner's own subjective memories or experiences with your own. "That's not what you really think." "You're wrong, that didn't happen." "That's not what you really feel."
One sign, by itself, does not necessarily mean you're a toxic person. However, the more signs that apply to you, the higher the chances that you are indeed toxic.