Trans Friend's Relationship

Listen up, buttercup. This joke is all about wordplay, see? The person's friend is trans, which means their gender identity is different than what they were assigned at birth. They're in a "polyamorous" relationship, meaning they're dating multiple people. The punchline is that if their partner had a dick, they'd be considered straight. It's funny because it plays on the idea of gender and sexuality being more complicated than just 'male' and 'female.'