Most lawyers are all too familiar with the following scenario: you are at a dinner party (or any other social setting) and you mention to someone you just met that you are an attorney. Instantly that person has a legal situation or problem that they want to tell you all about - despite your insistence that you are unfamiliar with the facts and/or that area of law. Imagine that this person's issue does happen to fall under your area of expertise, and they begin to share confidential information and asking more probing questions. Certainly you don't wish to be rude, but at what point does this conversation tread into dangerous waters?
Practicing attorneys must always be cognizant of who they are speaking to and what they are discussing - otherwise, he or she may find themselves inadvertently forming an attorney-client relationship through what seemed to be casual conversation, thus assuming a duty of confidentiality. The State Bar of California Standing Committee on Professional Responsibility and Conduct (COPRAC) addressed this issue long ago, in Formal Opinion 2003-161. The opinion lays out a variety of situations in which a lawyer-client relationship may have formed. An attorney-client relationship can be created expressly or impliedly - although an attorney has not explicitly assented to the relationship, a number of factors are considered in determining whether an implied in fact relationship exists.
The best strategy is one of caution. Rather than exposing your professional career to unwanted clients and liability for malpractice, be very clear in these types of situations that you cannot give legal guidance without a retainer agreement. Follow up conversations with emails, letters, or any concrete way to put these disclaimers in writing. There is no straightforward answer as to how to react to these scenarios, but being aware and careful is your best bet for protection.