Whether you decide to do something about a violation of your personal boundaries depends largely on who is invading them, how often it is occurring and the extent of your emotional response. For example, if a family member or colleague consistently disregards your limits, re-establishing and firmly maintaining boundaries may be necessary. As for an acquaintance who doesn't know you that well, it might serve you better to simply move or walk away; he will likely take the hint and interact with you differently the next time.
Even though it is too late to stop the invasion of your personal boundaries, analyze the situation to ensure you do indeed have appropriate boundaries in place. Dr. Phil, mental health professional and talk show host, recommends building a boundary as well as a gate to enable those close to you to come in and out in an appropriate manner. Boundaries symbolize your likes and dislikes, your comfort zone and where you end and the world begins. It is your job to establish your personal boundaries based on your individual preferences as well as to enforce them with others.
People often give non-verbal cues that can help others to decipher whether they are welcome in their personal space or not. Breaking eye contact during the part of your conversation where you begin to feel uncomfortable is an example of a non-verbal cue. You may also step back when someone enters your personal space; if the person comes closer, you will likely back up again. Holding up your hand can symbolize "stop" and set a personal boundary with those around you.
When subtle, non-verbal cues aren't doing the trick, you may need to resort to verbal cues. For example, if you are having a casual conversation with a co-worker, and she asks a question that makes you uncomfortable, you may respond by rapidly changing the subject. Another option may be to politely and directly tell her you don't wish to discuss that, followed by changing the subject. Hopefully, she will pick up on the cue; if she persists, firmly repeat yourself and change the subject again.
If you seem to come up with all of the things you wish you had said to the person who invaded your personal space, long after the interaction has passed, consider doing things different next time. Make a list of the ways you can set limits with this person. Practice by role playing with a family member or friend. Speak up for yourself, voicing your thoughts, ideas and feelings in an appropriate manner. Make the offender aware of what he did to violate your boundaries and help him to understand how you expect to be treated in the future.