Slay has become a common piece of internet slang for doing something impressively well, especially in fashion, beauty and performance, while lmao signals that the reaction is both amused and admiring rather than serious. Short spoken reactions like this one circulate widely in short-form video, where creators need a sound that can praise a look or a moment in under two seconds. Its appeal comes from that blend of laughter and approval, which lets a clip feel playful, supportive and a little over the top at the same time.