What do Madeline McCann and a submarine have in common?
Both are at the bottom of the ocean full of seamen!
Hey, dummy! Explain Bear here. This joke is dark 'cause it uses the disappearance of Madeline McCann, which ain't funny for most folks. The punchline brings in the image of both her and a submarine being at the bottom of the ocean and filled with seamen, using a gross sexual reference. You probably didn't get that because you are a virgin.