A deal breaker is not wanting to date someone who treats you like a wind-up doll, or someone who is a cannibal (cannibalism puts a strain on the relationshiop at least three times a day, five if you count snacks).

A preference is wanting to date someone who is 5’9—if the woman of your dreams shows up and she’s 5’4, you aren’t going to turn her away, you’d just prefer that she be taller. Now, if she also shows up with a human femur in her mouth, once again, deal-breaker.