What is unethically behavior?

Ethics and morality are subjects of great subjectivity. What one considers 'ethical' may not be, in another's opinion. However, there are common agreements about ethical behaviour, these are known as social standards. (Which may or may not include legal restrictions.)

Different traditions and cultures have their own sets of ethics. Christianity for example, has very distinct moral Codes of Conduct. Some of these relate to human relationships such as the principle of not engaging in sexual intercourse prior to marriage.

Hence, unethical behaviour is somewhat based on your own interpretations of moral standards. However, there are many commonly accepted unethical behaviours such as murder.