When someone asks, "What are you thinking?" you can respond with a touch of humor and light-heartedness with the following witty reply:
"Oh, you know, just plotting world domination and what to have for lunch. Standard stuff."
This response adds a playful twist and injects humor into the conversation while keeping things lighthearted and fun. Of course, choose a reply that aligns with your relationship with the person and the context of the conversation. The goal is to evoke a smile and create a pleasant moment.