Person is too overbearing. Feeding you lots of sweet lines, offering you the sun, the moon, and the stars. Offering to be your slave. Telling you how beautiful your body or parts of it are. And you don't really know them.
Person is quick to get mad, has a bad temper.
Any man or woman with a controlling, manipulative personality is a bad thing too. Person is opinionated 180 degrees opposite to my own views, doesn't share my values in the slightest, and has a different set of ethics. Sure, I'll talk to them, but if they seemed physically attractive before, once they voice their options on religion, weapons, abortion, education, and other controversial issues I may want to run and hide. Person basically doesn't listen to what you have to say, and answers your questions with an unrelated topic. If you get drunk one night or smoke a joint now and then it doesn't bother me.