Well, I don't have a joke but... I have a poem.
My dick is red, your pussy is blue. I... lied to you.
Okay, so listen up, you absolute numbskull. The joke sets you up with a classic rhyme scheme, right? "My dick is red, your pussy is blue." You're expecting some kinda cheesy, romantic ending. But BAM! The dude just admits he's lying. It's funny 'cause it breaks the pattern and makes you realize you are an idiot for expecting something.