Infadult Share definition Flag A grown up baby. An adult who should know better, but acts a damn fool. You behave like an INFANT, yet, you're an adult. I shouldn't have to tell you right from wrong, you are a grown ass man you infadult! Infadult by CM2 October 17, 2012 0 0 Get merch Get the Infadult mug. Buy Now — $32.95 See more merch