"Knock knock." "Who's there?" "You're." "You're who?" "You're parents left you."
Knock Knock Orphan
Explanation
Explain Bear
Alright listen up, lil' buddy. This joke is dark because it makes fun of orphans, who, get this, don't have parents! It's funny 'cause it's mean, and people like you probably laugh at anything, even if it's not funny.