The phrase "make top of one's head" refers to something that is done or said without any prior preparation or thought. Some synonyms for this phrase include "off the cuff," "impromptu," "spontaneous," "unrehearsed," and "ad-libbed." These words all suggest that something is being done or said without prior planning or practice. They are often used to describe someone who is able to come up with ideas or solutions spontaneously, without needing to carefully consider their options beforehand. Whether you're talking about public speaking, improv comedy, or just everyday conversation, having the ability to make top of your head remarks can be a valuable skill.