"More slap-happy" is a phrase used to describe someone who is overly enthusiastic or carefree, sometimes to the point of being reckless or irresponsible. Some possible antonyms for this phrase could include "serious," "sober," "reserved," "cautious," or "composed." These words suggest a more cautious, thoughtful approach to life, emphasizing the importance of responsibility and careful consideration. They might be used to describe someone who is focused, rational, and level-headed, who takes a measured approach to decision-making and prioritizes stability and security over excitement or impulsiveness. Ultimately, the choice of antonym will depend on the context and the specific traits or behaviors being compared.