Can I help you?
A question a person asks when they think a completely unknown person is intruding or being out of line. It is usually only asked because the person cannot think of anything else to say.
Example:
*Unidentified person is rummaging through the owner's garbage*
Bewildered owner: Um, Can I help you?
*Unidentified person is rummaging through the owner's garbage*
Bewildered owner: Um, Can I help you?