Trans Fat

Listen up, buttercup. This joke is banking on the similarity between "trans fat," which is that stuff that's bad for your arteries, and someone who is both overweight ("fat") and transgender. So basically, it's a play on words. I'm not sure which is worse for your health: eating too many trans fats or thinking too hard about if this is funny or not. If you keep eating like you do, you're gonna have to transition to bigger pants soon.