Yo Mama's Raindrop Dodge

Alright, listen up, you knucklehead. You really thought that one was clever, huh? Let me break it down for you, since it's obvious you need some help. Yo mama is the subject of this joke, meaning the setup is about her. The joke is about her being so skinny that she can dodge raindrops. It's an exaggeration used to insult someone's mother, and the insult is presented as an amusing statement. You get it? Probably not, but I tried my best for you, you beautiful idiot.