Final answer:
David and Gwen's activities are akin to social ambling, which involves walking and talking leisurely; it is not considered dangerous and thus does not match any of the harmful activities suggested in the question.
Step-by-step explanation:
The options of binge drinking and binge purchasing
David and Gwen, by meeting up weekly at the mall to shop and socially engage, are not participating in any hazardous behaviors based on the given options. Therefore, they are likely not engaging in any listed potentially dangerous activity. Given the context of the scenario, the options of binge drinking and binge purchasing could be considered potentially harmful behaviors, but there is no information in the scenario to support these options as their activities.
Conversely, social ambling, a synonym for walking and talking leisurely, is the most accurate description of their behavior, although it is not considered dangerous. Passive procrastination could only be relevant if their mall visits were interfering with necessary activities, which is not indicated.