The antonyms for the word "more slap happy" would be words that describe a more serious or composed demeanor. For example, "reserved", "dignified", "solemn", "stoic", "serious-minded", "somber", or "earnest". These words imply a sense of restraint, responsibility, and thoughtfulness, in contrast to the carefree and lighthearted nature of being slap happy. Antonyms like "melancholy", "gloomy", or "unhappy" might suggest a mood that is distinctly opposite to slap happy, reflecting instead a more muted or downbeat outlook. Ultimately, the antonyms for "more slap happy" are any words that denote a more sober and pragmatic attitude.