Crack up Definition 1 of 3Pro Tip 1/3Laughter Context Used after something is funny. It suggests uncontrollable laughter. The comedian’s pun was so good, the audience cracked up. Pro Tip 2/3Figurative Sense Doesn't always mean literal laughter—it can describe something very funny. That meme you sent me really cracked me up! Pro Tip 3/3Informal Setting Best used in casual conversations, not formal situations. After the funny story, even my boss cracked up.