A WeeWee Girl is a younger sibling that tends to annoy you. They are usually under the age of five years old and unpotty trained, often relying on their older sibling to help them go wee wee. Your younger sibling may only be referred to as a WeeWee Girl if you are ginger and/or obese.
Ginger Person: "My little sister is so annoying"
Cool Person: "Your sister must be a WeeWee Girl"
A generally undefined word that has no specific meaning, but is abstractly used as a response to any statement as a form of punctuation. G'WeeWee is a conversational dead end. It means nothing, yet it's the pinnacle of intellectual and comedic response. If you say anything at all, and someone responds with "G'WeeWee," you've essentially lost, and there's no coming back. It isn't insulting by any means, but it's purpose is to notify the person you're talking to that you're on a higher level than them. Note: typically used in conversation when discussing male-on-male sexual encounters.
"Hey dude, how are you? I'm so exhausted after work today."
"Me too, G'WeeWee."
"Haha Goku's so shredded, I wish I could lick his abs, and maybe do the same to Golden Freiza, G'WeeWee."