This paper proposes "perceptual multilingualism" as a research interest within the broader folk linguistic enterprise. By drawing on the geolinguistic mapping tasks popular in perceptual dialectology -- whereby participants are asked to draw and depict dialectal diversity in a given region -- we show that perceptual multilingualism can elicit knowledge and reasoning in the community about linguistic diversity more broadly. To do this, we analysed and discussed 41 perceptual multilingualism maps produced by high school students in Hong Kong about societal multilingualism across the Hong Kong region. On the one hand, the maps allowed us to quantify which languages manifest in the youths' metalinguistic awareness and where. On the other hand, we positioned the maps as discourses to be compared and analysed through a critical social theoretical lens. Doing so revealed implicit and contested power relations as they manifested in epistemic claims in dialectic relation to broader sociopolitical narratives in Hong Kong. This included Hong Kong's contentious transition to governance by Beijing and the marginalisation of the blue-collar workforce. Beyond the empirical metalinguistic data, our paper shows that perceptual multilingualism can contribute to critical sociolinguistics by helping to reveal power relations, hegemonies and ideologies, and resistance.