The rapid development and globalization of social media services such as YouTube has opened up new opportunities for informal learning, which are especially valuable to young English language learners in Asia, where opportunities for face-face-interaction with English-speakers have traditionally been limited. This exploratory study investigated language-related interactions in users‟ comments on a fansubbed video-clip of the 2008 Olympics song, Beijing Welcomes You（北京歡迎你）, from the perspective of informal teaching and learning. The study found evidence of potential teaching and learning episodes related to (a) translation, (b) language usage, (c) relationships between language and culture, and (b) teaching and learning processes, and pointed to several interesting avenues for further research on informal language teaching and learning in globalized online spaces.