Extensive and repeated language exposure is essential for second language learning. While not all learners can get such exposure routinely in face-to-face contexts, English language learners today create pathways to opportunities for learning English through participation in social media communities. The informal exposure to English they obtain can be driven by their passionate interest in popular culture and affiliation with communities of fans. The potential of interaction in online fandoms for language learning, however, depends in part on the language that learners are exposed to. In this study, a lexical bundle analysis was conducted to identify frequently used word combinations in YouTube comments posted under South Korean music band BTS fan-edited videos and performance videos. Lexical bundles retrieved from a corpus of 8,000 comments were investigated structurally and functionally. The bundles were found to display structural similarities with spoken registers, even though comments have unique textual characteristics. Functional analysis results showed that many of the bundles express interpersonal meanings, such as positive appraisal, with stance expressions. Findings from the structural and functional analyses of lexical bundles increase knowledge of the type of language that English learners are exposed to and can potentially benefit from by engaging in online fan communities.