Boundaries are the personal limits that, when appropriately instilled, demand respect from others. They can be physical, emotional, spiritual or sexual in nature. They can fluctuate throughout the course of a relationship and tend to vary from one relationship to the next. For instance, you may be comfortable with one friend borrowing your car but unwilling to do so with another friend who tends to be irresponsible. Because boundaries are so personal, there are no rigidly defined rules regarding which are acceptable. But there are basic guidelines common to healthy, functional friendships.

Physical Limits

There are some physical boundaries that are quite standard in relationships, particularly friendly ones. Abusive behavior, such as any unwanted sexual contact, hitting, punching, pushing and kicking are unacceptable. Many people also expect that their friends will respect their private spaces, such as bedrooms and backpacks. Hugs and other gestures of support and comfort are commonly acceptable depending on the level of intimacy in the friendship. Additionally, spending too much time together can violate the need for privacy.

Emotional Limits

Just as in the case of physical boundaries, actions and behaviors of others that are abusive are typically unacceptable. Name-calling, criticisms and unfounded accusations are examples of emotional manipulation. Some friendly relationships do allow for teasing, as long as the subject-matter is not a sensitive subject for the person on the receiving end of the joke. For instance, a close friend may laugh along with some teasing about a bad haircut, but be offended and hurt by a joke about an accomplishment she worked hard to achieve.

Spiritual Limits

Spiritual limits relate to the difference between appropriate and inappropriate conduct toward a friend's religious beliefs, states marriage and family therapist Darlene Lancer in her article for Psych Central, "What Are Personal Boundaries? How Do I Get Some?" They extend beyond religion, though, and encompass attitudes and actions that affect a friend's moral principles, values and overall sense of self. It would be wrong, for example, to deride someone who chooses to attend church or temple services.

Overextending friendship

Personal boundaries are not only about refraining from abusing or offending others, but also overextending yourself or trying to take care of them. It can be challenging to witness a friend who is in pain or otherwise struggling with problems in life. While it is a friend's role to offer support and encouragement, it is wrong to try to fix someone's problems. Rescuing others from their turmoil is not helpful to them because it prevents them from taking responsibility for themselves.