Sticking one's head inside a microwave oven is extremely dangerous and can cause severe harm or even death. Microwaves emit electromagnetic radiation specifically designed to heat food, and they are shielded to prevent this radiation from escaping and causing harm to humans.
If a person were to stick their head inside a microwave oven while it is operating, the microwaves would not selectively brainwash them or have any mind-altering effects. Instead, the primary risk would be exposure to high levels of microwave radiation, which can cause severe burns to the skin and other tissues, including the brain. Additionally, the confined space and lack of oxygen inside the microwave can lead to suffocation and other serious injuries.
It is crucial to prioritize safety and follow proper usage guidelines for any electrical appliances, including microwave ovens. Never attempt to put any part of your body inside a microwave or interfere with its operation while it is running.