My girlfriend's name is Candice.
Can these nuts fit in your mouth? :D
Candice
Explanation
Explain Bear
Alright, listen up, buttercup. The joke is a play on words. The dude's girlfriend is named Candice. When you say "Can these nuts," it sounds like "Candice." Then he's asking if his "nuts" (you know, his family jewels) can fit in her mouth. I bet you didn't even notice that you can't spell, huh?