咩 (me1) is the Cantonese question word 'what' - a contraction of 乜嘢 (mat1 je5). 搞咩 literally 'do what' is sharp and often accusatory, the Cantonese twin of Mandarin 搞什么 / 闹哪样.
culture
The character 咩 borrowed sheep-bleating onomatopoeia (baa) for the question word because the sounds happen to match in Cantonese. You'll see 搞咩 in HK internet comments the way English has 'wtf'.
