think twice about something/about doing something
To reconsider, be cautious about, or thoroughly contemplate something before committing to it. I'm going to sue them for everything they're worth—maybe then they'll think twice about trying to steal my ideas! Maybe we should think twice about investing so much money in a project we know so little about.
think twice about someone or something
to give careful consideration to someone or something. Ed may be a good choice, but I suggest that you think twice about him. You will want to think twice about it.