One warning sign in a relationship is physical abuse. Physical abuse is threatening or hurting one of the people involved in the relationship. This can include hair pulling, punching, slapping.
Bullying can also be a a sign of an unhealthy relationship. Bullying involves humiliating or embarrassing a person. There is more than one type of bullying. The diffrent types are Verbal, physical, cyberbullying.
Being dishonest in a relationship can be another warning sign of an unhealthy one. It includes someone being deceitful in their character or behavior. This can be shown in lying, being defensive.