In Taiwanese Mandarin internet slang, 虾米 is a playful way to say 'what?' — it comes from the Hokkien/Taiwanese pronunciation of 啥物 (siánn-mih), which sounds like 'shrimp.' Think of it like a bilingual pun.
usage
As a food ingredient, 虾米 refers specifically to tiny dried, peeled shrimp used in Chinese cooking for umami flavor, distinct from 虾仁 (xiārén, peeled fresh shrimp) and 虾干 (xiāgān, larger dried shrimp).
