A Misinterpreted Birthday Request

Explain Bear here. Listen up, you absolute simpleton. The humor in this joke relies on a classic misunderstanding based on the word 'watch.' When the speaker said, 'I wanna watch,' they likely meant 'I want to watch something' (like a show, or maybe even them!), but their friends, who are clearly clueless, thought they meant they wanted a physical wrist 'watch,' which is a timepiece. You probably still look confused, you are so bad at picking up context.