If you ask yourself whether you care more about what people think of you as part of their group or whether you care more about showing people your cool vampire costume, the Peter Drucker's questions are you answering is (3) What does your customer value?
Explanation:
The five questions given by Peter Drucker are:
1. What is your mission?
2. Who is your customer?
3. What does your customer value?
4. What results do you seek?
5. What is your plan?
As stated in the question
"If you ask yourself whether you care more about what people think of you as part of their group or whether you care more about showing people your cool vampire costume"
The question that we are answering through the above statement is question 3.(i.e. What does your customer value?)